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String Trimmer (Strimmer) Won't Work - 2-Stroke Engine and Carburetor Troubleshooting

Two-Stroke carburetor
Two-Stroke carburetor | Source

String Trimmer Won't Start?

String trimmers, also known as line trimmers, weed eaters, weed whackers, strimmers and whipper snippers, can be troublesome garden tools, and difficulty in starting is often due to an issue with the carburetor (carburator)
In this article, I strip and clean a carburetor and point out where problems can arise. While I specifically deal with the carburetor from a trimmer, carburetors on other 2-stroke engine powered machines such as brush cutters, hedge cutters/trimmers, chainsaws, consaws and leaf blowers are similar.

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Thanks!

Common Reasons Why a String Trimmer Won't Start

Difficulty in starting can be due to an issue with:

  • A dirty or cracked spark plug
  • The magneto not generating a spark
  • Venting of the cap on the gas tank
  • A blocked fuel filter
  • Clogging of the carburetor from gum deposits due to gas being left in the tank over winter
  • A worn diaphragm or pump in the carburetor
  • A stuck valve in the primer bulb or leaking bulb
  • A blocked spark arrestor screen

Usually though, the problem is caused by parts which wear out or become compromised in some way in the carburetor. Before jumping to conclusions and starting to troubleshoot, follow a proper start sequence.

What's a Carburetor?

Two stroke engines on trimmers and also four stroke engines on lawn mowers, generators and other small equipment are fitted with a device called a carburetor (often shortened to carb in North America or carby in Australia). Engines in older cars and other gas powered vehicles also had a carburetor before the introduction of fuel injection in the 80s and 90s.
The function of the carburetor is to mix a mist of gasoline and air together to form an explosive mixture which is burned in the cylinder of the engine. Air is drawn by suction from the engine through a tube in the carburetor. This tube, about 1/2 to 3/4 inch in diameter on a small engine, has a narrowed section called the venturi. As air flows through the venturi, it increases in speed, and pressure drops below atmospheric. The drop in pressure causes fuel to be drawn through a jet into the air flowing through the venturi. This jet works exactly like the spray nozzle on a garden hose and a mist or spray of gas is created, which mixes with the airflow. (Paint spray guns used off a compressor work on the same principle). The mixture flows out of the carburetor and into the engine through the intake manifold, eventually ending up in the cylinder where it is burnt.

Two-Stroke (Two-Cycle or 2T) Engines

Two-stroke (also known as two-cycle or 2t) engines are used on most hand held garden power tools. They have several advantages over four-stroke engines (like the one in your car or lawn mower). Firstly there is no sump or reservoir on the underside, filled with oil for lubricating the engine. A sump would be impractical considering that such hand held garden power tools may be used upside down and at all angles. Small 4 stroke engines are fairly "primitive" and don't have an oil pump, relying on a "splasher" or "flicker" on the connecting rod to throw oil onto the piston and other moving parts. So this system would be ineffective on a 2 stroke engine if it was used upside down. To lubricate these type of engines, you need to pre-mix oil with gas. The absence of a sump and its oil content reduces weight. Also 2-stroke engines don't have valves, a cam shaft or the other bits and pieces which operate the valves, instead they have "ports", or entry and exit slots for fuel/air mixture and exhaust gases. This further reduces weight. So the result is a lighter machine, a higher power to weight ratio than 4-stroke, no requirement for an oil change and less working parts to wear out or fail.

The greatest disadvantage of these types of engines is that because oil is burned in the combustion chamber or cylinder along with the gas, they are smelly and produce smoke (which causes pollution in cities where scooters and motorbikes are the main means of transport). Low smoke 2-stroke oils are available however, which somewhat cuts down on emissions.

How to Fix a String Trimmer

This is a bargain basement trimmer I bought in a large home store. Unfortunately spare parts are unlikely to be widely available for repairing such a model (although the store may be able to get them from their supplier), which is probably mass produced in China. Still it was cheap and I've got years of use out of it with no engine problems (the protection guard for the line broke though and I had to make a new one). If you want a machine to last for 10 years or more, go for a model by a well known manufacturer such as McCulloch, Stihl, Husqvarna, Poulan Pro, Oleo-Mac, Ryobi, Craftsman, Weedeater, Flymo or Honda. That way, you can be certain of getting service information, spare parts and other after sales support.

Typical gas string trimmer
Typical gas string trimmer | Source
2-Stroke trimmer engine
2-Stroke trimmer engine | Source

Warning - Gas is Flammable

Gas (petrol) is flammable. Keep all sources of ignition away from where you are working on an engine. This includes, naked flames, cigarettes, hot surfaces and tools which generate sparks (e.g. angle grinders). Rags soaked in gas can ignite, so dispose of them safely. Store gas in metal jerry cans or plastic containers made for the purpose. We have all stored gas in old plastic oil containers or similar. There is however always the danger of static from these containers igniting the fuel. Don't leave cans in full sun when in use, instead store them in the shade and keep them away from the hot exhaust of an engine.

How to Mix Fuel for Two-Stroke Engines

Lubrication of 2-stroke engines is effected by mixing 2-stroke oil with gas before use. In general, the oil to gas ratio for a 2-stroke engine should be 1:50. This equates to 20 ml per liter (litre) or 2.6 fluid ounces (US) per gallon (US). Some manufacturers recommend a 1:25 ratio for their engines so check your manual. 1:40 is probably a good compromise. Try to avoid fuels which contain ethanol as this absorbs moisture over time, oxidizing metal surfaces. Swirl the mixture in the container for a few seconds to mix it thoroughly.

You can normally buy 100 mL plastic bottles of two stroke oil which is sufficient to make up 5 litres of mix. In the US, 2.6 fluid ounces bottles of oil are available for making up a gallon of mix. If you do a lot of trimming, obviously it's more economical to buy a larger bottle of oil.

Gas and Two Stroke Oil Needed for a 50:1 Ratio

Amount of Fuel Mixture Required
Gasoline/Petrol
Two Stroke Oil
1 Litre
1 Litre
20 ml
5 Litres
5 Litres
100 ml
1 US Quart
1 US Quart
0.64 US Fluid Ounces (about 1.5 tablespoons))
1 US Gallon
1 US Gallon
2.6 US Fluid Ounces

Starting a Trimmer, Hedge Cutter or Chain Saw Properly

Priming the Carburetor

Before you start your engine, you need to prime it. The priming bulb sucks fuel up into the carburetor which may be empty from the last time the engine was run. The priming bulb must be pushed about ten times to suck in sufficient fuel. Make sure there is enough fuel in the tank before you do this so that the filter on the end of the fuel line is submerged and you're not just sucking air into the priming bulb.The engine only needs to be primed again after a tank refill, if it has been a long time since the trimmer has been used and the carburetor has drained, or if the trimmer was used upside down for an extended period and the engine cut out. The filter on the fuel line is normally able to move around in the tank, so that even when the trimmer is used upside down, the filter falls down into fuel. However if there isn't much fuel in the tank, sometimes this doesn't work, so the intake line can get drained and filled with air as the engine uses up fuel, requiring a re-prime. Try to keep the tank at least half full.

Starting the Engine

Rest the machine on the ground, clear of any debris and start the engine on full throttle with the choke on. Once the engine gives a kick, give it another pull and if it runs, wait until it cuts out, or for about ten seconds, whichever comes first. (If it doesn't start after a few pulls, try re-priming). Then turn off the choke and allow the engine to continue running (or try starting again if it had cut out on-choke). If the engine won't start, repeat the process from the start by turning the choke back on, priming the engine, and pull starting. If after several attempts at starting, nothing happens, the engine may have flooded. Leave it for about 10 minutes for fuel to evaporate before attempting a re-start.
If the engine has been run in the last 10 minutes or so and is hot, you don't need to turn the choke back on before re-starting.

Note: There is some variability in the starting procedure for these type of engines. Some engines don't have a primer bulb. Also an engine may have both a partial and full choke position. The choke may be arranged so that you start the engine without squeezing the throttle and revving it, only doing so when it fires up. Revving then automatically knocks off the choke. Check your manual if possible for details.

Try Pouring Some Gas into the Cylinder

A traditional way of getting an engine to start is to pour a little gas into the spark plug hole. I emphasize a little!, about a thimble full or a soda bottle capful. Try not to spill it on the outside of the engine. Screw the plug back in and start the engine on full choke. This often helps to get a stubborn engine running. Don't try this if the engine has been running and hot, because the gas could potentially ignite if you spill it. A less messy option if you have a section of fuel or narrow gage air line is to dip it in gas to a depth of about 2 or 3 inches, put your thumb over the top, stick the end of the line into the plug hole and take away your thumb, allowing the gas to run out.

Empty Fuel Lines Can Cause Difficult Starting

If you run the engine until it cuts out before re-filling, the fuel lines will have thoroughly emptied out. Remember you need to push the primer button 5 to 10 times before starting the engine again. If the check valve in the primer button isn't the best, this can cause difficult starting. If the button is working properly, it should feel "spongy". Keep pressing it until it fills with gas and most of the air bubbles are gone. You can check whether the primer is working ok by partially filling the tank with gas but allowing the end of the line without the filter to remain above the surface (the line with the filter should be submerged). When you repeatedly push the primer button, gas should flow out of the line without the filter.

Maybe There's a Problem With the Spark Plug?

Could be! Remove the plug with a spark wrench, push the plug lead back onto it and hold the metal part of the plug against the engine body. This can be somewhat difficult to do with these engines as a plastic cowl usually covers the engine and it can be difficult to access the metal body. You could use a bolt, small tin or whatever to make contact. Switch on the starter switch, hold the plug by the rubber booth at the end of the spark lead and pull the starter cord/rope. This can be difficult to do single handed unless you are an octopus, so find a trusty assistant to help you! A healthy spark should be blue, it might be difficult to see the spark in bright sunlight, so move the trimmer into the shade or indoors. If there's no sign of a spark, try a new one or even a plug from a lawn mower (to test the ignition circuit is ok) before you attempt any more in depth troubleshooting (Don't use a plug which is longer than the original one as it could hit the piston!)

Dirty or Cracked Spark Plug

If the plug won't spark, there are two possible causes:

Cracked Plug A crack in the ceramic insulation of the plug can cause the spark to take a "short cut" through the insulation so that it doesn't jump the gap where it's supposed to do

Dirty Plug If the ceramic insulation which surrounds the central electrode is excessively covered in soot, again this can short out the spark so that it won't jump to the outer electrode (the one connected to the threads). You can clean soot off with a tooth brush, or better still a "toothbrush" style, small wire brush. Then scrub the electrodes using the toothbrush in a small bowl/coffee jar lid full of gas.

When undoing the spark plug, hold the wrench with two hands so that it doesn't slip off the plug and damage it
When undoing the spark plug, hold the wrench with two hands so that it doesn't slip off the plug and damage it | Source
Use a socket or whatever to make contact with the body of the engine when testing for a spark
Use a socket or whatever to make contact with the body of the engine when testing for a spark | Source
A "toothbrush" style wire brush is useful for cleaning soot from a spark plug
A "toothbrush" style wire brush is useful for cleaning soot from a spark plug

Could There Be a Problem With the Ignition Module?

As explained in great detail in my hub Lawn Mower Won't Start? - Top 10 Mower Troubleshooting Tips , small engines have a device called a magneto for creating a spark at the plug to ignite the fuel/air mixture in the cylinder. This is a cross between a transformer and generator, and creates voltages of about 10kV. These are normally electronic capacitor discharge ignition modules (CDI) on modern trimmers, so there are no points to be cleaned or a condenser (capacitor) to replace. If you don't get a spark at the plug and have tried a new plug and checked for loose wiring without success, this module may be at fault and need to be replaced. Alternatively the embedded magnets on the flywheel may have weakened, or the gap between poles of the coils and flywheel may be off. This should be approximately 0.006 inches.

Electronic ignition module - When the kill switch is open circuit (on position), engine runs. Closing the switch cuts the engine
Electronic ignition module - When the kill switch is open circuit (on position), engine runs. Closing the switch cuts the engine | Source

Testing the Kill Switch

The kill switch shorts out the magneto to cut out the engine. Dirty or corroded contacts usually result in an inability to stop the engine rather than a problem with starting.

You can check the resistance of the switch with a multimeter set to the ohms range. If you don't know how to use one, read How to Use a Digital Multimeter (DMM) to Measure Voltage, Current, and Resistance

This should change from infinite resistance when the switch is in the on position (when the switch is disconnected from the engine) to less than an ohm in the off position. Normally a switch should have a high resistance when off, but remember in this arrangement "off" refers to the engine switched off and the switch contacts closed.

Ideally you should detach one of the leads from the switch when testing the resistance in the on position because the resistance of the ignition module in parallel will affect readings. If the resistance is several tens of kilo-ohms however, this is ok because it means the switch is opening and not shorting out the ignition module. See this link for details on how to use a multimeter:


Remove the switch with a screwdriver
Remove the switch with a screwdriver | Source
Set the meter to the "ohms" range. Resistance should be less than 1 ohm with the switch in the off position. Ideally you should detach one of the wires from the switch when testing.
Set the meter to the "ohms" range. Resistance should be less than 1 ohm with the switch in the off position. Ideally you should detach one of the wires from the switch when testing. | Source

Multimeters from Amazon

Useful for Checking Voltage, Current, Continuity and Fuses. You can buy a cheap meter like the Etekcity one below which will do the job adequately, or alternatively a more expensive model like the Fluke 113 which is recommended for general purpose home/auto maintenance. By paying more you get better accuracy, plus the option of getting the meter calibrated/repaired.

What About the Cap and Check Valve on the Gas Tank?

Unlike lawn mowers and other such yard equipment which is normally used in one orientation, trimmers, chainsaws and hedge cutters must be used at all sorts of angles. A lawn mower has a vent in the gas tank cap to allow air into the tank as gas leaves it. If the tank wasn't vented to atmospheric pressure, this would restrict the flow of gas out of the tank. (Turn a large soda bottle filled with water upside down and you'll see what I mean). 55 gallon oil drums also have a secondary bung which needs to be loosened to vent the drum, enabling smooth flow from the main outlet during emptying. On a lawn mower, the vent is just a hole, with a fiber or plastic baffle inside the cap to stop gas splashing out. This isn't good enough on a trimmer if the tank is turned upside down, so a one way valve (check valve) is used. This may be fitted in the cap of the gas tank or on the body of the tank itself. The valve allows air in but gas can't leak back out. This could get clogged with dirt, so try starting the engine with the cap slightly loosened (keep the tank upright) to see if it makes any difference. To clean the valve, gently slide a small flat blade jeweler's screwdriver into it to make sure its clear (Make sure it's small diameter to prevent damage). I couldn't get access to the back of this valve because a fuel filter was pushed into place. There wasn't a problem with the valve so I didn't go any further.

On my trimmer, the one way valve is fitted in the gas tank cap
On my trimmer, the one way valve is fitted in the gas tank cap | Source
This valve holder has a filter at the back. It seemed to be difficult to prise out and may have been bonded to the holder, so I left it in place
This valve holder has a filter at the back. It seemed to be difficult to prise out and may have been bonded to the holder, so I left it in place | Source

Could the Fuel Filter Be Dirty?

Possibly. I've never had any problems with clogged filters on my hedge cutter, chain saw or trimmer, and they have have had hundreds of hours of use. Whether the filter gets clogged depends on the quality of the gas you get from your gas station and your environment. If you don't take care when filling the tank and allow crap such as dirt and sand into it, it will inevitably end up in the filter. Impurities in two-stroke oil probably accumulate in the filter also. If you can prime the engine ok and fuel can be seen to return to the tank via the line without the filter, the filter is unlikely to be clogged.
The filter is located on the end of the intake fuel line and is replaced rather than cleaned (although you could try removing it, wash in hot water plus washing up liquid, rinse and allow to dry before replacing)

Now It's Time to Remove the Carburetor From the Engine

Your carburetor may be somewhat different from the one below but the basic principle is the same. A section of membrane in the carburetor acts as a pump. Pulses of low and high pressure from the engine crankcase move this membrane backwards and forwards, and this sucks gas from the tank to a reservoir pocket in the carburetor. Reed valves act as check/one way valves to stop gas flowing backwards. A needle valve operated by a diaphragm regulates flow into the reservoir pocket, and shuts off flow when the pocket is full. A primer bulb is included which helps to suck fuel up into the carburetor before starting. Without this, the starter cord would have to be pulled multiple times to fill the carburetor with gas. Some carburetors don't have this primer button arrangement.
It's a good idea to lay out parts on a piece of cloth or old towel to stop them rolling about during dismantling. You can also store them in a magnetic parts tray.
Don't work outdoors like I did while disassembling. This was only to facilitate taking photos in good lighting conditions. If you drop small parts on a lawn, you will probably never find them!
If you have an air compressor and blowgun, blow away any grime form the outside of the carburettor before removing. Do this before removing the air filter and fuel lines so as to avoid blowing grime into the carburetor or bursting the diaphragm inside it.

Magnetic parts tray. A cloth also stops parts rolling about
Magnetic parts tray. A cloth also stops parts rolling about | Source
Drain the gas tank
Drain the gas tank | Source

First Remove the Air Filter

Remove the air filter from the housing and check it for dirt. Wash it out in washing up liquid and hot water.

Filter Housing
Filter Housing | Source
Foam air filter
Foam air filter | Source
Ensure the filter is free of dirt. Wash if necessary
Ensure the filter is free of dirt. Wash if necessary | Source
The choke is simply a plate which covers the air intake. When it is closed, the engine sucks in a richer mixture (i.e a higher concentration of fuel in the air/fuel mixture). This makes for easier starting
The choke is simply a plate which covers the air intake. When it is closed, the engine sucks in a richer mixture (i.e a higher concentration of fuel in the air/fuel mixture). This makes for easier starting | Source

Remove the Air Filter Housing

Two nuts hold this housing in place.

Remove the retaining nuts with a socket wrench
Remove the retaining nuts with a socket wrench | Source
The carburetor exposed - Next the fuel lines and throttle cable must be removed
The carburetor exposed - Next the fuel lines and throttle cable must be removed | Source
Mark the fuel lines before removal. A "Tippex" style correction pen is useful for doing this
Mark the fuel lines before removal. A "Tippex" style correction pen is useful for doing this | Source
Don't stretch the fuel lines by pulling them. Instead, try pulling them gently while pushing with a flat bladed screwdriver or needle nose pliers against the edge of the lines
Don't stretch the fuel lines by pulling them. Instead, try pulling them gently while pushing with a flat bladed screwdriver or needle nose pliers against the edge of the lines | Source
Remove the end of the throttle cable
Remove the end of the throttle cable | Source
Carburetor ready for dismantling
Carburetor ready for dismantling | Source

Carburetor Disassembly

The diaphragm and reed valve pieces are delicate so take care while handling.
It's also a good idea to take lots of photos at every stage of disassembly just like I did here, in case you forget how to put everything back together!

4 Screws hold the carburetor together. Remove the primer bulb retaining plate
4 Screws hold the carburetor together. Remove the primer bulb retaining plate | Source

Check the Primer Bulb for Any Holes

The primer on a two stroke engine is used for sucking fuel up into the carburetor. Without the primer bulb, the starter cord would have to be pulled loads of times before the fuel lines and carburetor fill up.

Holes or splits can eventually form in the primer bulb. If this happens when the bulb is full, you'll probably notice it because gas will leak out. However if it has been some time since the trimmer was used and the bulb has emptied out, any holes will likely prevent it sucking fuel up from the tank. If the material of bulb has deteriorated, it's possible also that it won't seal properly against the body of the carburetor, resulting in an air leak. Again this will prevent the bulb sucking up fuel.

A check or non return valve is part of the priming system (the red piece in the photos below). This has two one-way sections. When you push the primer bulb, fuel flows from the bulb through the central one-way section to the carburetor (Which according to Wikipedia is a duck bill valve). Fuel can't flow back because pressure squeezes the "duck bill" closed. Dirt in this valve can keep it open, allowing fuel to flow back to the primer bulb, so the carburetor doesn't get properly primed. The outer section is known as an umbrella valve and the floppy outer edges prevent fuel flowing backwards. When you release the bulb, suction causes the flexible edges of the valve to rise and fuel enters the bulb. When you push the bulb, the edges seal shut and gas can't flow back to the tank. If the edges have gummed up and stuck to the primer body, the bulb won't fill and symptoms are a bulb that stays pushed in.

Trimmers either have a primer button mounted on the carburetor or a remote primer
Trimmers either have a primer button mounted on the carburetor or a remote primer
Primer bulb and one way "umbrella" check valve (red piece in center). Check the edges of the valve aren't stuck to the primer body.
Primer bulb and one way "umbrella" check valve (red piece in center). Check the edges of the valve aren't stuck to the primer body. | Source
One-way or check valve. Check there's no dirt stuck in the "duck bill" valve section in the center
One-way or check valve. Check there's no dirt stuck in the "duck bill" valve section in the center | Source

Fuel Flow Through Carburetor

With all the holes and passageways in the carburetor, this can be somewhat confusing to work out. Have a look at the photo below. This is the sequence:

Fuel leaves the tank via the fuel line (the one with the filter) and enters the carburetor, flowing up through the screen filter at point 1.

Fuel flows down passageway at point 2.

Fuel flows back up at point 3. The reed valve prevents fuel flowing back.

Fuel flows down at point 4 and into the compartment 5. Here it is pushed by the "pump" (which is just a flexible section of the gasket) to point 6. Another reed valve prevents it flowing back when the pump is sucking fuel from the tank.

Fuel fuel flows into the reservoir pocket (on the underside of this half of the carburetor) via the valve at point 7. The needle valve in this brass piece is operated by the diaphragm (see explanation of diaphragm below)

Finally fuel leaves the reservoir pocket via the cross shaped piece in the center, and sprays into the carburetor venturi through the jet (in the other half of the carburetor)


Fuel Pump

Fuel is pumped by suction from the crankcase acting on a membrane The pulses of pressure move the membrane backwards and forwards, sucking fuel. Reed valves prevent fuel flowing backwards. Handle this piece with care as it can be easily damaged.

Note: In the photo below, this appears to be one piece. However if you zoom in, you can see that there are in fact two parts stuck together. Firstly a gasket (which makes contact with the numbered part of the carb) and secondly a part which has the valves and pump.When reassembling, it's important to replace these in the correct order to prevent leaks.

Reed valves and fuel pump. The red numbers are the sequence of ports through which the fuel passes, flowing up through the screen at 1, and exiting down through the metering needle valve at 7 to the reservoir pocket.
Reed valves and fuel pump. The red numbers are the sequence of ports through which the fuel passes, flowing up through the screen at 1, and exiting down through the metering needle valve at 7 to the reservoir pocket. | Source

Carburetor Kits

If you have a trimmer made by a well known manufacturer, the chances are that you will be able to buy a carburetor rebuild kit. This is a collection of parts which can be used to replace components in a carburetor which have become torn, worn out, warped, punctured, coated with hard deposits or deteriorated in any other way to the extent that cleaning won't help. It usually comprises of gaskets, reed valve/pump piece, diaphragm, needle valve, springs, primer bulb etc

The other half of the carburetor. Part of the jet assembly is in the center
The other half of the carburetor. Part of the jet assembly is in the center | Source

Diaphragm on a 2-Stroke Engine Carburetor

Lawn mowers and other similar engines often have a float bowl and float.This acts in a similar way to a toilet cistern and ball cock valve, ensuring there is always a full reservoir of fuel at a constant level from which the jet is supplied with fuel. This is important for the speed behavior of the engine. Unfortunately a float bowl and float rely on gravity for correct operation and this system can't be used on a trimmer which is used in all orientations. Instead, a reservoir compartment is built into the carburetor. Once this fills, pressure on a diaphragm, activates a metering lever/rocker arm, forcing a needle into a seat, cutting off flow. As fuel is used, the reservoir begins to empty, lessening the pressure on the diaphragm, and the metering lever opens the needle valve.
Just like the reed valve piece, this is delicate and needs to be separated carefully from the body of the carburetor, especially if it has become stuck.
Over time the diaphragm can become punctured or get stretched and "baggy" in which case the needle valve can stay shut, even when the reservoir pocket is empty. The material can also stiffen, preventing proper operation.

Diaphragm

The diaphragm. This normally pushes down on the lever/rocker arm opening the needle valve. As the pocket under the diaphragm fills with fuel, pressure on the diaphragm causes it to bulge out, allowing a spring to close the needle valve
The diaphragm. This normally pushes down on the lever/rocker arm opening the needle valve. As the pocket under the diaphragm fills with fuel, pressure on the diaphragm causes it to bulge out, allowing a spring to close the needle valve | Source
Check for holes by holding up against a bright light source. Warping of these delicate parts can also prevent them working properly
Check for holes by holding up against a bright light source. Warping of these delicate parts can also prevent them working properly | Source
The diaphragm assembly consists of a needle valve, metering lever/rocker arm and spring
The diaphragm assembly consists of a needle valve, metering lever/rocker arm and spring | Source
Remove the retaining screw
Remove the retaining screw | Source
The needle valve seat. Clean this with carburetor cleaner
The needle valve seat. Clean this with carburetor cleaner | Source
Needle, metering lever and spring
Needle, metering lever and spring | Source

Clean All Surfaces

Clean all surfaces with a carburetor cleaning aerosol. This removes any gum deposits which can clog pathways and jets. If you have a compressed air blow gun, you can use it to aid drying. Set parts aside to dry once cleaned. Plastic parts, especially the reed valve piece and diaphragm should be dried immediately after cleaning as the solvents in carburetor cleaner can be harsh and dissolve the plastic. Avoid bending the reed valves with the force of the jet by spraying gently or resting the piece on a flat surface.

Clean the fuel pathways with carb cleaner. Make sure the outlets are pointed away from your eyes
Clean the fuel pathways with carb cleaner. Make sure the outlets are pointed away from your eyes | Source

Long Lasting Trimmer Line From Amazon

This 0.095 inch diameter (2.4mm), 3 pound, 685 foot spool of professional trimming line by Oregon should last you years and years. According to Amazon, it has a high strength inner core and an outer coating to prevent welding. In other words adjacent turns on a wound spool are less likely to stick together as the line unwinds from the spool.
Check your trimmer to see whether it is compatible with this diameter line.

Clean all surfaces of the carburetor with carb cleaner
Clean all surfaces of the carburetor with carb cleaner | Source
Clean the jet. An air blow gun is invaluable for clearing a complete blockage in the the jet if you don't have any carb cleaner.
Clean the jet. An air blow gun is invaluable for clearing a complete blockage in the the jet if you don't have any carb cleaner. | Source

Re-Assemble The Carburetor- How to Reconnect the Fuel Lines

Once everything has dried, re-assemble the carburetor. If you forgot to mark the fuel lines, you can check whether you mixed them up by filling the tank so that only the line with the filter is submerged or pulling the line without the filter up out of the gas in the tank. What should happen when you press the primer bulb is that gas is sucked through the line with the filter on the end, through the carburetor and flows back to the tank via the other line without the filter. If the lines are mixed up, air gets sucked up into the carburetor and you will see this bubbling out through the filter.

Fuel lines in tank, the intake line has a filter
Fuel lines in tank, the intake line has a filter | Source

Blocked Spark Arrestor Screen in the Muffler (Silencer)

The muffler exhaust is fitted with a wire spark arrestor screen (so you don't set fire to your garden or start a bush fire!). Over time this collects smuts and can get clogged, reducing power output of the machine. Low smoke 2-stroke oil supposedly slows build up of carbon. If you add too much two stroke oil to your gas however, the engine will smoke and deposits of soot will accumulate more rapidly. I have checked this screen on my trimmer every couple of years and have never seen any deposits worth talking about. In any case you can clean the carbon deposits with an old toothbrush, compressed air, or a small wire brush.

Remove the cowling
Remove the cowling | Source
Remove the cover over the exhaust outlet
Remove the cover over the exhaust outlet | Source
Spark arrestor screen
Spark arrestor screen | Source
Clean the screen with an old tooth brush, wire brush or compressed air
Clean the screen with an old tooth brush, wire brush or compressed air | Source

Adjusting the Idle Speed

If the engine keeps cutting out when idling, the idle speed may be too low. Allow the engine to run at top speed for about a minute, then release the trigger. Turn the idle speed screw clockwise about one eight of a turn and wait to see if the engine continues to run without cutting out. If it still cuts out, turn the screw another eight of a turn. Some trimmers and all hedge cutters have clutches which prevent the cutting head from operating when the engine is idling. If the blade starts moving or the trimmer line starts spinning, turn the screw slowly back counterclockwise until movement stops.

Adjusting the idle speed
Adjusting the idle speed | Source

Trimmer Won't Stop

If the start/stop switch fails on your trimmer (or other engine), turn on the choke. This will flood the engine and stop it promptly.

Trimmer Cuts Out on Full Throttle

  • Check the vent in the cap/tank isn't blocked
  • Ensure cracks in intake fuel line in tank aren't sucking in air, preventing fuel from getting to carburettor
  • Make sure choke is off
  • Are you using the correct mixture? Use 1:50 or 1:40 oil:gas. Too much oil can cause problems
  • Clean air filter and exhaust screen
  • Diaphragm/pump section in carburettor may have stiffened so it can't pump/meter fuel

Did You Get Your Engine Started Using the Information in This Article?

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Did You Find This Article Useful?

Was the info in this article useful and instructive? How can I improve it? Would you like to ask me any questions?

Please provide some feedback below, and also I would appreciate it if you could pin it on Facebook or Pinterest.

Thanks!

© Eugene Brennan 2015

HubPages in no way endorses this article.

Further Reading and Related Links

You may also be interested in some related articles:

How to Use a String Trimmer Properly - Without Breaking the Line!

Lawn mower won't start? - Top 10 mower troubleshooting tips

Choosing and buying a lawn mower - electric, gas or battery?

In the US, Carb Tech Solutionstock carburetors and rebuild kits for trimmer and mower carburetors

In the UK, Garden & Hire Spares Ltd supply carburetors, carburetor parts and spares for garden equipment



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More by this Author


Comments 110 comments

Randy Godwin profile image

Randy Godwin 2 years ago from Southern Georgia

A very concise article detailing proper maintenance and repairs to 2 cycle engines and not only weed trimmers. the carburetors on these engines are notorious for becoming gummed up while being stored over the winter months while not being used.

Having these engines serviced by a repairman will often cost more than a new trimmer depending on the problem one is having. Congrats on a well deserved HOTD.


eugbug profile image

eugbug 2 years ago from Ireland Author

Thanks Randy, much obliged for the comments!

Starting one of these engines can be frustrating if it misbehaves, and frantic pulling of the starter cord can eventually end up in it snapping, which adds to the frustration!

Thanks again!


Randy Godwin profile image

Randy Godwin 2 years ago from Southern Georgia

Unfortunately this HOTD will probably not get much hub love because most of the hubbers here are ladies, eugbug. The men will probably love it though. I'll surely refer back to it shortly when the grass is growing in full swing. Keep up the good work! :)


eugbug profile image

eugbug 2 years ago from Ireland Author

At the risk of getting some flak, maybe I should make the hub pink, then the ladies might like it!!! (like those pink cordless tools for women!)


Randy Godwin profile image

Randy Godwin 2 years ago from Southern Georgia

I tried writing a few hubs especially for the ladies--one was about hunting knives and survival tools, and some were indeed pink--but they didn't seem to do well at all. Perhaps it was my approach? :o


Hady Chahine profile image

Hady Chahine 2 years ago from Manhattan Beach

Super-informative hub! Lately I've been experiencing problems with my Stihl gas powered edger. Although it's 10 years old, it is still a quality piece of equipment. Anyway, it takes for ever to get it started. Of course I didn't keep the owner's manual, so troubleshooting it has become a guessing game. But, thanks to you I will print this article and use it to my advantage. - Thumbs up!


eugbug profile image

eugbug 2 years ago from Ireland Author

Thanks Hady! This is the page for downloading manuals from Stihl USA. You might find a copy of instructions for your edger there:

http://www.stihlusa.com/manuals/instruction-manual...


Scott 2 years ago

This is great information! Thank you!


eugbug profile image

eugbug 2 years ago from Ireland Author

You're welcome Scott, thanks for the comments! There are lots more articles like this one on HubPages, and on many other topics, so come and visit again!


wdonn73 2 years ago

wdonn73 been reading about the strimmer rebuild superb detail in every way, I have just purchased a larger brush cutter/strimmer got it together yesterday and was all set up to cut some long grass, started the engine tic over fine until I tried to speed up and all I got was putputptpt and stop did not matter what I did it would not increase speed put in new petrol mix today and now the primmer bubble will not inflate after the first push, checked everything, any Ideas would be most helpful.


eugbug profile image

eugbug 2 years ago from Ireland Author

Firstly, try to run the engine on full choke for longer before you rev the engine (about 10 seconds). From my experience with 2-stroke engines, it is often necessary to switch back and forth between full choke and no choke before the engine will continue to run. So if your engine cuts out when you speed it up, switch the choke back on and try starting again and when it runs for 5 to 10 seconds, only then turn off the choke. If it cuts out again, turn the choke back on and so on...

If the intake fuel line runs dry, it can some times be a little difficult to prime it again. As I suggested in the article, take the cap off the tank and fill it so that the return line is above the level of the gas. This allows you to see whether priming is actually working, and gas is flowing through the lines and back to the tank. Make sure of course also that you have sufficient fuel in the tank so that if you use the trimmer at an angle, the filter on the intake line is submerged.

If you purchased a new trimmer, there is unlikely to be an issue with blocked fuel lines or faulty fuel valves. Check your manual to make sure you are following the startup procedure correctly.

Hope this helps!


wdonn73 2 years ago

Thanks for the early reply, I had run the engine for a good five minutes before taking it out to the field, I also tried putting some mixture into the carb to see if it would run long enough to lift fuel from the tank, but no good, will fill the tank and try what you suggest will try to add some fuel into the feed pipe to see if that helps, will try tomorrow ,thanks again for your help.


Sid Wright 21 months ago

Very helpful indeed. I was about to dump the "!$@ thing. I read your article and decided ti give it a try. Must have been a bit of dirt along the way somewhere, and the needle was a bit 'stuck'.

Thanks for your help!


eugbug profile image

eugbug 21 months ago from Ireland Author

Thanks Sid! The motto is "Fix it, don't dump it" . (Sorry, I can't think of anything to rhyme with "fix"!)


jason 20 months ago

hello there,i have a mculloch trimmer ,but the cord keeps tangling in the machinee


eugbug profile image

eugbug 20 months ago from Ireland Author

Hi Jason, can you provide me with more details?

If by cord you mean the trimmer line, it can tangle if you don't take care when winding the spool. Make sure you wind it tightly and evenly and don't bunch all the line up at one end of the spool. Also the knife on the guard should cut the line, otherwise the line can extend too much and get tangled around stuff.

The starter pull cord may tangle if the spring tension is insufficient to wind it tightly around or into the reel when it retracts Also if there's any grime, resin or tar on it, it might bind.

Have a look at this guide for replacing a cord on a Stihl trimmer:

http://hubpages.com/living/Stihl-KM-56-RC-Trimmer-...


Jan 18 months ago

First of all, I greatly appreciated this article when trying to make my weed eater run again. It's very detailed and instructive!

However, within this type of carburetor, there is another needle/screw not covered by this tutorial. It's going through the pivot screw in the accelerator lever (black plastic part) on the carb and through the rotating barrel-ous part inside the carb body, and usually, it's sealed. The previous owner of my weed eater has, unfortunately, removed the seal and tinkered with the screw. The engine still ran quite ok when I purchased it, but the screw has come off its proper position due to engine vibration (and then due to my efforts...). Now, it just won't start, no matter what I do. Do you happen to have an idea what should be the basic adjustment point for that particular needle? Many thanks in advance!

Jan/Prague/Czech


eugbug profile image

eugbug 18 months ago from Ireland Author

Hi Jan,

Is the screw located in a similar position to the one in the photo above, which shows the throttle cable being removed? Its the silver one just under the screwdriver blade. This is the idle adjustment screw stop. If its turned counter clockwise too far, the engine won't stay idling. Firstly make sure that you try to start the engine with the throttle trigger fully squeezed. This will prevent the idle screw from having any influence on the engine. Run the engine for a minute and release the trigger. Turn the screw counter clockwise 1/8 turn at a time so that the engine idles smoothly, or if the weedeater has a clutch, the trimmer head is just about to turn.

If this doesn't work, the chances are that the screw is the mixture adjustment screw. On some engines there are two of these for adjusting the low speed mixture and high speed mixture, marked "L" and "H" respectively. If the engine only has a high speed adjustment, you could try and turn the screw in until it reaches the end of its travel (don't tighten to avoid damage). Then unscrew about 1 1/2 turns and use this as a base point for getting the engine started. Once the engine starts, run it at full throttle. Adjust the screw 1/8 turn at a time counter clockwise until it starts to cut out. Next turn it clockwise until it begins to cut out again. Set the screw midway.

There may have been a gasket/seal on the mixture screw threads, typically a flat rubber washer. A suitably sized O-ring may work as an alternative.

What's the make/model of the machine. I may be able to find a manual/adjustment sequence online for it.


lyoness913 profile image

lyoness913 18 months ago from Overland Park, KS

You wouldn't believe how helpful this hub was to my husband. He's not a writer, but he says to tell you thank you for taking so much time and putting so much detail into this hub!


eugbug profile image

eugbug 18 months ago from Ireland Author

Thanks Wendi, glad it was of use to him!


Nick 18 months ago

Great instructions, easy to follow. I've stripped and cleaned the carb, the strimmer starts well but won't hold high revs. Thanks for any ideas.


eugbug profile image

eugbug 18 months ago from Ireland Author

Thanks Nick. Does it cut out immediately when you open the throttle? Sometimes when starting these engines, they will out after you try to rev after turning off the choke. (or when you attempt to re-start with choke off after the engine gives a kick with choke on). If this is the case, turn the choke back on and try starting and run for another few seconds before switching the choke back off. I'm not quite sure why this is. Possible its because the engine isn't quite warmed up, or because the reservoir compartment discussed above isn't quite full initially, and the jet in the carburetor can't feed enough gas into the venturi when the throttle opens up and airflow increases.


Nick 18 months ago

Thanks for the fast reply Eugene. I noticed the post above but it's not that in my case, the motor starts easily and ticks over nicely, allowing the revs to increase slightly until properly warm. As background, it's been working perfectly but then slowly developed the fault. At first I'd leave it on tick over a second or two then it would rev ok but the time it would work between 'rests' got shorter until now it won't take full revs at all, almost as if there's a fuel pump that can't quite keep up with demand. I've checked the plug and exhaust, both seem ok. :-(


eugbug profile image

eugbug 18 months ago from Ireland Author

I agree with you that it may be a fuel pump issue. Try running the engine with the tank cap loose to eliminate any problems with air failing to flow into the tank, which could restrict fuel flow out of the tank. Sometimes the check valve is located elsewhere on the tank rather than in the cap. Check also the passageway to the crankcase isn't blocked by debris or the edges of any gaskets. Suction from the crankcase pulses the pump in the carburetor.

Is there a high speed mixture screw which can be adjusted?


Nick 18 months ago

Cheers, Eugene. I've already tried with the cap almost off and replaced the fuel filter. Yes there's a mixture screw, it hasn't been altered and is one and a half turns out, I haven't tried adjusting it. I don't think it's the pipes as fuel pumps through well with the primer. Maybe I need a carb rebuild kit so the membrane and diaphragm can be replaced. It's a Mac Allister machine btw.


Nick 18 months ago

Correction: It's a Dynamac machine, not Mac Allister, that's the chainsaw!


eugbug profile image

eugbug 18 months ago from Ireland Author

I'm not familiar with how these mixture screws work and whether there's a needle valve on the end which screws into a seat. You could try screwing it out completely and check whether anything has built up on the needle over time. Screw it all the way in first to check that its exactly 1 1/2 turns out before removing so that you can put it back to the way it was.

Is the reservoir/metering pocket similar to the one in the photos above?

It would be interesting also to try priming as you rev. If this works ok, it would point to the pump being at fault.


Nick 18 months ago

I'd checked the needle and it looked ok but guess you never really know how well it's metering the fuel. It does look very similar to the carb above. Mine is actually a Walbro WYK carb, I found the service manual here: http://www.walbro.com/media/21913/WYKseries.pdf Ran through everything again, mixed up a fresh batch of fuel at exactly 50:1 and it's running perfectly once more. Thanks for all your help and suggestions, been a Godsend!


eugbug profile image

eugbug 18 months ago from Ireland Author

Great! There's nothing better than an engine which you've being working on for an eternity suddenly springing to life. Thanks for letting me know Nick! (Now if only I could get this cement mixer engine working...Groan.....)


Bob 18 months ago

I have what seems like the exact same carb as you - i opened it up, cleaned it ( including behind the gauze fule filter ) and put a fresh set of gaskets in but it's leaking fuel out through the air filter a bit and will only start for a few seconds when the tank is empty it will run for about 15 seconds with the last bit of fuel in the carb - I'm certain I put it together properly and that it was clean - have you any ideas - I was wondering if the tightness of the bots could be a contributing factor - is there a torque setting - also the shaft of the outside of the duckbill valve was slightly torn but I didn't think it would stop the engine running like this - I'd be happier to actually replace the carb at this stage but I can't find a replacement here ( europe ) that I'm confident will work. Thanks for your post.


eugbug profile image

eugbug 18 months ago from Ireland Author

Hi Bob.

There may be a torque setting for the bolts if you can find this info somewhere in a service manual, but generally I tighten screws or bolts until there is a lot of resistance, but try not to over do it. This skill comes with experience. When tightening a bolt there is usually a "crack" sound as the bolt stick-slips. Then it is adequately tight. You can wring bolts by over tightening, but usually this happens when trying to undo a rusted bolt. Anyway, tighten screws in a staggered sequence, i.e, tighten diagonally opposite pairs. Since screws/bolts are steel and the carburetor is a a soft alloy (zinc/aluminium), don't overtighten as you can strip threads.

As regards the tear in the duck bill valve, the same thing happened to me. If you have nimble fingers you can glue it with superglue. Allow the petrol to dry off and bleed super glue into the tear from the tip of a pin. If you get this wrong it can seal the duck's bill closed, so be careful, and maybe stick something such as a jeweller's screwdriver through it to keep the two halves open. If it doesn't look as if the tear is an issue, it's probably better to leave it alone. The duckbill's function is to act as a check valve to stop fuel flowing back from the reservoir to the priming bulb when you release the button. Once the engine runs, it doesn't do anything. You could try to prime for longer, maybe 20 pushes. If the valve is only partially working, the reservoir pocket may eventually fill.

If fuel leaks out the air filter, the carburetor might be just flooding. Studying my photos above, I can't see anywhere fuel can get into the carburetor other than through the jet. (I'm not sure what the cross shaped part numbered 4 in the photo above does. This could be a filter)


Sharif 17 months ago

Good day can u help me with my carb its always over flowing . Same carb with the picture


eugbug profile image

eugbug 17 months ago from Ireland Author

Hi Sharif - Check there are no holes in the diaphragm/gaskets by holding up to the sky.

Make sure the needle valve and seat it pushes into are clean. Also check the air filter isn't dirty.

Check also that there is no fuel leaking from the gas tank cap or where fuel lines exit the tank. Depending on what angle you are using the trimmer, sometimes fuel can run from these regions down onto the carburetor making it look as if gas is leaking from the carb or air filter.


chezchazz profile image

chezchazz 17 months ago from New York

Timely (my string trimmer broke last weekend) and thorough (with your help I was able to fix it). Thank you!


eugbug profile image

eugbug 17 months ago from Ireland Author

Your welcome Chazz and glad it was of use!


Tom evans 17 months ago

was very helpful answered all the questions I was thing of and more it was like having a mechanic standing next to you with advice, as good as reading a haynes manual for my bikes and cars. well done, good stuff.


Daithi Byrne profile image

Daithi Byrne 16 months ago

Hi, having trouble with a strimmer. It starts when primed but cuts out when held in normal position for strimming but when I turn it up over my head it starts to come back - after it dies it needs to be primed again to start have u come across this problem?


eugbug profile image

eugbug 16 months ago from Ireland Author

Hi Daithi. First check there's no issue with the filter on the end of the line coming up out of the fuel (or catching on the return line) when you re-orient the machine. If the filter comes up out of the fuel for several seconds, and fuel drains out of the line, this can rapidly stall the machine. So try filling the tank fully. Also when the engine starts and the choke is turned off, I find its a good idea to run a machine on full throttle for about ten seconds before starting to cut. This gives it time to stabilise and the the carburetor fills properly. It could also be something to do with the pump/reed valves in the carburetor, so when you turn it up over your head, fuel is running down into the carburetor rather than being pumped.


Daithi Byrne profile image

Daithi Byrne 16 months ago

Will check that later , thanks


Rico One 12 months ago

I have been searching for this information in this format for months. I've taken my equipment in for service and the cost seemed high. I feel confident that I can now handle common maintenance of my yard tools.

Thank you!


eugbug profile image

eugbug 12 months ago from Ireland Author

You're welcome Rico, thanks for the comments!


Dennis Bening 11 months ago

Best article I've found on how to troubleshoot a 2 cycle carb. My old McCulloch leaf blower runs like new !! Thank you !!


eugbug profile image

eugbug 11 months ago from Ireland Author

You're welcome Dennis! Glad it helped you get your machine working!


George 8 months ago

Very helpful


Jean-Louis 7 months ago

10 months ago Jan/Prague/Czech spokes about another needle/screw not covered by this tutorial. It's going through the pivot screw in the accelerator lever (black plastic part) on the carb and through the rotating barrel-ous part inside the carb body, and usually, it's sealed. ...... Do you happen to have an idea what should be the basic adjustment point for that particular needle?

Your responses seems to be out of concern; you don't relate to the screw of Jan but to the idle screw

Can you give us more information about that needle screw that is located axially in the barrel, only screwable by a tiny screw driver through the central hole of the yellow screw used as rotation shaft of the command lever ( just below the end of the screw driver on your above picture "Remove the end of the throttle cable".

May be, this "needle-screw" is used to adjust fuel/air mix at middle run.

If possible, please precise the basic adjustment point for that particular needle.

Many thanks in advance!


eugbug profile image

eugbug 7 months ago from Ireland Author

Hi Jean Louis, What is the model/make of the trimmer? I might be able to source a manual. However, if the machine is running ok, its better not to fiddle too much with the screw. Also if the high speed mixture is too lean, it's possible to exceed the speed rating of the engine, causing overheating and damage. Sometimes there is a "H" or "L" marking near the screws, indicating they are for adjusting the high and low speed respectively. As a starting point, screws should be screwed in gently until the hit the bottom of their travel (don't screw tight to avoid damage). Next unscrew them one complete turn. This is the base point. Run the engine at full throttle for a couple of minutes until it is warmed up. To adjust the high screw, run the engine at full throttle and turn the screw clockwise until the engine runs poorly. Next turn it anti-clockwise until it begins to run erratically again. Set the screw a little to the left of midway between these two limits. To adjust the "L" screw, allow the engine to idle and follow the same procedure as above, setting the screw about 1/8 turn anti-clockwise of the midway position.


Nick 7 months ago

Hi,

If you're a forgetful idiot and you forget to add the oil to the petrol.....run the engine and then it dies what would be the likely damage caused ?

The engine still turns so I don't believe I have frozen the engine....I have now added the correct oil mix to the petrol.....I have spark....I have tried putting a thimble of petrol into the sparkplug chamber but not starting....

I checked the exhaust system and cleaned it.....

When it turns over sometimes smoke comes out of the exhaust

I now have the carb off and apart at the moment....terrified as I've never attempted anything like this before.....

Would I have caused terrible damage ?


eugbug profile image

eugbug 7 months ago from Ireland Author

Hi Nick, as regards damage, it probably depends on how long you ran the engine for, but if it turns ok, it's not seized. Forgetting the petrol shouldn't do any damage to the carburettor and even if the engine overheated due to lack of lubrication, the carburettor is separate from the engine block and shouldn't suffer heat damage. The engine may have overheated excessively which could have damaged the seal between the crankcase and engine block or crankcase cover and block (if block and crankcase are one piece), preventing crankcase compression. See the link at the top of this page which explains how a two stroke engine works. Some engines have a poppet intake valve which allows fuel into the crankcase and maybe this has gotten stuck or damaged from overheating. When you pull the start cord, is there much resistance? If it pulls much easier than before, maybe the cylinder/bore have worn, reducing compression. If you're adventurous, you could try opening the crankcase and investigate whether there is any damage to the valve. On my trimmer four screws hold an access cover to it (See photo with caption "Remove the cover over the exhaust outlet"). However before you do any of this, make sure the engine is priming ok by checking that fuel returns to the tank when you push the primer bulb several times and follow the proper startup procedure.


eugbug profile image

eugbug 7 months ago from Ireland Author

This link shows the damage to a piston if you use neat petrol: https://www.youtube.com/watch?v=t001qQJ3ZtE


Ben 7 months ago

Thanks for a great clear and informative article!


Terry 7 months ago

I am tired of fixing gas engine carburetors. I buy electric products anymore. Problem solved. Electric weed eater. Electric mower. Electric chain saw. Electric tiller (small one, still have a large gas one). Government regulations have totally screwed up small gas engine reliability with complication.


eugbug profile image

eugbug 7 months ago from Ireland Author

There is some truth in that and an electric tool is also less likely to give trouble. 99% of the time it will start ok too. However there is the obvious disadvantage of a trailing power cord (unless you choose a battery model), and electric tools have less power for a given size than their gas counterparts.


Matt Man! 7 months ago

Howdy, I need that exact carburator for my boat engine! I bought the engine from a coworker and he is no longer with my company. I can't locate a part number. Can you tell me? I can't believe you were working on the exact one!!! Please help. Thanks!


eugbug profile image

eugbug 7 months ago from Ireland Author

Hi Matt. I don't think there were any model numbers or other marks on this carburetor, it was from an unbranded Chinese trimmer. Will check though. Are you sure this is the exact same carburetor? All these devices look very similar. For instance this one: http://ebay.to/1OlixxD which has a 10mm inlet bore. Don't know whether it would work though. The side which couples with the air filter is a little different. Also the hole spacing for the mounting bolts might not be the same. If you search for "trimmer carburetor" on eBay, you'll get lots of results and some products are generic, and not for any specific model.


Jan Nienaber 6 months ago

Hi Guys. I bought a wolf chainsaw china made. It work well for 2 days. From the outset it dit not prime properly. Now it doesnt prime at all. It has 3 pipe inlets at the carb. Will one be air? At the fuel inlet it has good fuel at pressure but it doent reach the outlet. It is brand new. I cant see ant damage to the pipes or the primer bulp. Could you help me. Thank you.


eugbug profile image

eugbug 6 months ago from Ireland Author

High Jan. If it's new and still on warranty, make sure to bring it back. If there are 3 fuel lines, you may have a remote primer. See the diagram above for an explanation on how the system works. The air intake is visible once you remove the air filter. When you say it has good fuel at pressure, what do you mean? If you try to prime the machine, fuel should flow back into the tank via the return line. Make sure when you prime that there is sufficient fuel in the tank so that air doesn't get sucked into the intake line. The result is that it can then take lots and lots of pulls of the starter cord to get the machine working


Jan Nienaber South Africa 6 months ago

Wow thank you for your response. Yes the primer bulb sit on the tank not on the carb. I can hear the primer action in the tank and if i open the cap i note bubbles. No fuel flows trought the carb. You may prime a 100 times ....nothing. If i pull the inlet line off the carb fuel actually burst out of the pipe at pressure. I rather should take it back.


eugbug profile image

eugbug 6 months ago from Ireland Author

Have you checked for a spark? Did you use the recommended amount of two stroke oil in the mix? Squeeze the throttle trigger fully when starting and make sure the choke is on. Sounds like you may have a dud machine though because it should at least give a kick. It's probably best not to mess about too much with the trimmer if you're going to take it back.


Jan 6 months ago

Yes i did it worked in the beginning. I think it is a airlock or a blockage somewhere. I will take it in and will let you know. Thank you Eugene i appreciate your help.


eugbug profile image

eugbug 6 months ago from Ireland Author

No problem! The engine could also be seriously flooded if you pulled the starter cord loads of times. If you haven't done so, leave it for about 10 minutes before reattempting a start.

P.S. Just remembered something. I'm thinking trimmer but I forgot you have a chainsaw. Usually a chainsaw is started with the chain brake engaged and no throttle, not full throttle as I stated earlier. If the engine has a decompression valve, it should be opened. However, your chainsaw may have an automatic decompression valve, or none at all. Checkout the start procedure for a Stihl chainsaw which has full choke, half choke and run positions built onto into control lever. Your machine may be somewhat different though.

http://www.stihl.co.uk/step-by-step-starting.aspx#


Jan Nienaber 6 months ago

Thank you sir. I given it back for repairs. Will let you know


Jan Nienaber 6 months ago

Hallo Eugene. Got my chainsaw back. Remote primer bulb replaced works like a bom. Thank you for your advise. Take care


eugbug profile image

eugbug 6 months ago from Ireland Author

Hello again Jan! So everything worked out fine in the end. Thanks for letting me know the outcome!


Ben Lewin 6 months ago

Thank you for your informative page.

what should be the compression PSI for the string trimmer?


eugbug profile image

eugbug 6 months ago from Ireland Author

Hi Ben, thanks for the comment.

The consensus seems to be that pressure should ideally be in the 90 to 120 PSI range. However some people reckon that pressure can be as low as 70 PSI. Here's a link where compression values are discussed: http://bit.ly/1sQeCoc


Mario Rincon 6 months ago

Hello Mr. Brennan...

I just wanted to ask you the name of the trimmer (brand, model, etc.) that you used during this article.

Thank you.


eugbug profile image

eugbug 6 months ago from Ireland Author

Hi Mario! Unfortunately this was a trimmer which was badged/branded by a homestore. It was manufactured in China but the store won't give me any info on who their supplier is.

If you're referring to using a part from the carburetor, take a look on eBay. There are lots of very similar looking carburetors to the one which is used on this trimmer.

I'll have to delete your comment because I don't think comments can display personal information such as emails.

Hope this helps!


Mario Rincon 6 months ago

Hello Mr. Brennan.

Thanks for answering my comment. I'm looking for the check valve of the carburetor (the red piece) to be specific. I know there are more like this out there, but I just wanted to know where I can find exactly this one. If you do know, please let me know to my email if you still have it. If not, I'll monitor the comment section to hear back from you. After that, you can delete your response once I confirm that I saw it.

Thank you.

This red piece is for my summer intern project by the way.


eugbug profile image

eugbug 6 months ago from Ireland Author

Have a look at this eBay link: http://ebay.to/1XdDva4

If you search on eBay for "string trimmer check valve", there are lots more like it.


Mario Rincon 5 months ago

Thanks so much!

You can take my comments off if you want now.


Paul 5 months ago

Hi, I have an issue with my trimmer. It will not start. When I prime it for starting, fuel immediately comes out of my air filter. I have not taken apart the carb yet, I'm assuming something is clogged. Could the return fuel line be causing this?


eugbug profile image

eugbug 5 months ago from Ireland Author

Hi Paul, I've been thinking about this and trying to envisage what scenario would cause this issue. If you read and followed the details above, you will know that when the primer bulb is released, fuel is sucked up around the edges of the red valve into the bulb. When the bulb is pressed, fuel leaves the bulb through the centre of the valve and returns to the tank. Meanwhile, the carburetor can "tap into" this fuel (on the intake side of the valve) and take a feed through the screen filter. Possibly the edges of the red valves are not sealing properly so that when the bulb is pushed, fuel is forced back into the intake line (the one with the filter). Because the line has a filter on the end of it, this would restrict the flow back, pressure would rise in the line and fuel could take a shortcut into the carburetor and flow through all the passageways, into the "reservoir pocket" as I described it and then out via the jet into the venturi. If the tank is pressurising because the vent valve isn't working properly (the one in the cap or tank body), this would compound the problem. Try loosening the fuel tank cap and see if it makes any difference and then take a look at the valve in the primer to see whether there is anything gumming it up or stopping it from sealing.


Stuart Rodger 5 months ago

Hi Eugene,

I made the mistake of buying a cheap Chinese Imported Brushcutter Strimmer Chainsaw combination.

It was very difficult to start first time, but did work in strimmer mode.

When I changed over to brushcutter it starts with much perseverance but stalls on full throttle and will not start again. I have checked everything on your list, and when I put some neat petrol in the spark plug hole, it starts but then quickly stalls after about 30 seconds, so just burning the fuel I have added. I have stripped the air filter off the carb and cleaned out some leaf particles but generally looked ok. I notice however that the inlet behind carb into engine block, which is plastic secured by two socket head capscrews is loose. How do I get to this to tighten, without removing and dismantling carb? I think it may be sucking air into cylinder at this connection ?


Stuart Rodger 5 months ago

On further investigation I saw that the carb just sits on top of the manifold and is sandwiched by a gasket when the air inlet and choke plate are bolted on. When I lifted off the carb assembly I could access the manifold bolts and found that one was almost completely loos and the other was not even hand tight. After tightening and re-assembly I found the engine starts and runs fine. Clearly the bolts had not been properly tightened at the factory! Another issue I found though when rebuilding, is that the markings for choke open and closed are the wrong way round ! So when I thought I was starting on choke I actually had choke fully open and when closing choke on hot engine it was stalling. This had also been contributing to the difficult starting even before the manifold bolts came loose.

Now I know to operate back to front (;-)


eugbug profile image

eugbug 5 months ago from Ireland Author

Hi Stuart, glad it worked out ok!

If anything is loose on an engine, the problem can worsen over time as vibration shakes fasteners, and nuts/bolts can totally undo themselves. Star washers should prevent loosening, but unlike the case with lock nuts, once the head of a bolt becomes loose, a star or spring washer won't work. The hex socket head screws on your trimmer may have been buried in a recess without any washers so they could have loosened themselves. Loctite Threadlock or similar is useful for preventing this sort of thing happening.

Anyway thanks for sharing this, it's just one more thing which others can check out when troubleshooting their machine.


Chris 5 months ago

Really useful article. Just gone through a week long learning process for servicing my hedge trimmer. I think taking things apart should be a last resort.

My engine was cutting out when pressing the throttle for higher revs.

I bought carb cleaner. Sea foam and a new spark plug.

emptied of fuel. Pressed primer to remove even more.

1. Cleaned air filter as per ur instructions.

2 sprayed carb inlet with lots of carb cleaner. Pointing upwards and a little bit at a time and turned it over to suck it through. Left for 10 minutes. Turned over engine, will fire and run whilst it fires.

3. Did same for sea foam then removed spark plug and filled cylinder with sea foam. Put back spark plug and leave for one hour. Emptied, then replaced fuel. replaced air filter. Pulled over several times. Then ran smokey for a while, but idling perfectly and revs fine.


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eugbug 4 months ago from Ireland Author

Thanks Chris, I agree dismantling should be a less resort. It requires discipline and care if you don't wan't to end up with "spare parts" left over and no where to put them!


Nick 4 months ago

Eugene, you are more hero. Cleaned the carb like you said, needed to replace one of the fuel lines, but my budget strimmer seems to be running again.. Thanks so much for your clear instructions.

I do have an issue with my large Stihl bushcutter, though: it will not start again if I stop it after it's got warm...Any ideas? Nick


eugbug profile image

eugbug 4 months ago from Ireland Author

Hi Nick, thanks for the comments!

Is the choke definitely off when you try to re-start? I haven't come across this problem personally, but it sounds like the carburetor is flooding. Another suggestion I've come across is that pressure could be building in the tank. This wouldn't be so much an issue when the machine is running but once it stops, pressure would force fuel past the needle flooding the carburettor. You could try loosening the tank cap and see if it resolves the problem. Then checkout the vent in the cap or tank to see if anything is clogging it. It's possible also that the plug is sooting up from using fuel with excess two stroke oil in it. Again the engine might run ok, but once it stops, the spark could be too weak to get it going again. Apart from that, the issue could be with ageing of the carburetor pump/diaphragm. This might stretch/warp as it gets hot so that it doesn't work properly.

Can you re-start the brushcutter when its allowed to cool down?


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Nick Mifsud 4 months ago

Definitely no choke on and it starts fine when it's cooled down.

It used to conk out quickly after it got warm and I thought blowing some air into the fuel cap seemed to help, it goes much longer now (about 25 mins)...so I guess it could be related.

Now I've the confidence, I'll strip it down and give it a good clean.

Nick


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eugbug 4 months ago from Ireland Author

If blowing some fuel into the cap works, it sounds like a fuel pump problem, the air possibly helping to force fuel into the carburetor. Don't (I've learned the hard way!) blow compressed air into a carburetor before it's dismantled because it could burst the diaphragm or do other damage.

Engines with clutches driving the cutting head can conk out when idling if the springs in the clutch are dodgy, causing the shoes to move out erratically, stalling the machine.

Does priming the engine when hot make any difference and help starting?


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Nick Mifsud 4 months ago

I blew air into the fuel cap to clear a possible blockage in the valve in the cap which might have been causing suction...

Machine idles fine and I've kept the clutch well greased.

One other thing...as I sense it's about to conk out (power drops off) a couple of nudges of the primer bulb keeps it going for another 5 to 10 mins...does that provide a clue?

Priming the engine does not help after it's gone out and when it's still hot.

Nick


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eugbug 4 months ago from Ireland Author

My hedge trimmer has similar symptoms, when it's idling, speed slowly drops off and a nudge of the throttle or primer bulb keeps it going for another while. I still think it's something to do with the fuel pump or possibly the fuel filter is blocked (priming would charge the carburetor with fuel, but the pump might be unable to maintain the diaphragm "reservoir" in a filled state and it would eventually empty. However have you tried running it with the cap slightly loosened to eliminate a problem with the valve in the cap?


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Nick Mifsud 4 months ago

Hi Eugene,

Back home. Stihl FS120 rubbish today so I stripped it down and cleaned it.

First problem: can't find the spark arrestor screen anywhere (suspect this might be the culprit).

But major issue: the starter rope won't turn the crank shaft, which has very little movement either way. Really confused.... Am I missing something obvious?

Thanks,

Nick


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eugbug 4 months ago from Ireland Author

Hello Nick, page 9 of this service manual shows the spark arrestor:

https://www.scribd.com/doc/140934817/FS120-FS200-F...

Page 30 has some details on the recoil starter and they recommend lubricating with a few drops of kerosene. I would remove the complete starter from the engine and investigate whether it's the starter which has seized up and wont turn, or the engine. It's always a good idea also to wear safety glasses if you're doing any work on a starter, e.g. when replacing a rope. If the spring pops out suddenly, it could cause a serious eye injury.


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Nick Mifsud 4 months ago

Thanks...looks like there never was an arrestor plate fitted!

Return starter seems fine. It's the flywheel that simply won't budge (it moved a little before it stopped moving at all). Really weird as I didn't touch it at all...

Suspect next step (next weekend) is to take it off and see what's going on behind it...

Nick


John keating 3 months ago

Thank you Sir this article has been very helpful.


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Nick Mifsud 3 months ago

Hi Eug,

Back after a 4 week spell away.

So worked out the flywheel problem: I hadn't replaced the ignition coil box firmly enough and so the magnetic force had wedged it into the flywheel.

But when I tried to turn it again it wasn't turning smoothly. Removed the spark plug and it turned fine and I have a good spark.

Replaced spark plug and same problem - difficult to turn and no sign of it starting.

Any ideas?

Thanks,

Nick


eugbug profile image

eugbug 3 months ago from Ireland Author

Hi Nick,

Is the ignition coil definitely tightened on its mountings and not rubbing against the flywheel? (the magnet could still be pulling it in as it passes). The combination of friction from a rubbing coil plus the force required for compression in the cylinder could be making the whole thing difficult to turn.

Before you tighten the coil, you should slide something in between it and the flywheel magnet. The gap is supposed to be between 0.2 and 0.3 mm or the thickness of a business card. I don't know where you're located Nick, but if you're in Europe (assuming you are because you call it a strimmer!), Lidl often sell vernier callipers which are a very handy measurement tool for checking thickness/size of big and small things. Anyway press the coil gently against the spacer and tighten. Then replace the spacer. The only other thing which would make the flywheel hard to turn is a hydraulic lock when the cylinder partially fills with petrol. Since fluid can't be compressed, the piston wouldn't move. However you would notice all this petrol when removing the plug.


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Nick Mifsud 3 months ago

Thanks for the quick reply! I'm in Scotland btw...

I'll check I've got the correct gap tomorrow, I think I do since it turns just fine when the plug's out and the spark is good...

Like you say, no sign of too much fuel...but I'll double check in daylight.

Thanks again...


eugbug profile image

eugbug 3 months ago from Ireland Author

Just had a thought, the plug could be hitting the piston and preventing it from reaching the top of the cylinder. Did you by any chance use a longer replacement plug? Also if you forgot to replace the washer on the plug, the extra couple of mm could be allowing it to reach further into the cylinder.

Is the flywheel hard to turn just at one point in its circle, or right through 360 degrees?


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Nick Mifsud 3 months ago

The saga continues.

Flywheel turning okay, plug okay and sparking but no ignition, even though fuel seems to be coming through.

Added a cap full of petrol into the cylinder (just to check) and replaced the plug...still no sign of life...

Take it I've a compression issue...or am I missing something else...?


eugbug profile image

eugbug 3 months ago from Ireland Author

Hi Nick, I think it's becoming an epic at this stage!

Is the flywheel now turning ok with the plug replaced? Do you think the plug could be hitting the piston? I had another brainwave that maybe there was an issue with a decompression valve not working, but it seems the FS 120 doesn't have one of these valves fitted.


Nick Mifsud profile image

Nick Mifsud 3 months ago

The plug wasn't the issue...but I changed it because I had a spare...

I've tightened everything up....

...suspect I'm going to admit defeat and take it in...:(


Nick Mifsud profile image

Nick Mifsud 3 months ago

Now I'm really confused: back home this weekend and the machine started! It wasn't idling well and once it's gone out I can't restart.

I've increased the idling speed a touch and will try again tomorrow, but suspect still have the ORIGINAL issue..i.e. Can't restart it after it goes out after running even for a short while (30 seconds).

Conclusion: new carb required?

Nick


eugbug profile image

eugbug 3 months ago from Ireland Author

Is the engine still hard to turn Nick? I'm working on an engine at the moment from a cement mixer (actually it came from a lawn mower, but that's a long story!). Anyway engine died during mixing concrete (very frustrating). Then I spent day and days trying to fix it. It would run ok for about 15 seconds and then cut out. After being left for a few seconds, it would run again but keep cutting out. When it cut out, it seemed to be difficult to turn and squeaked a bit. So I dismantled the engine and it turned out that the oil flicker, a sort of scoop device attached to the connecting rod and used on most small engines to throw oil over everything, had broken off. So the crankshft/connecting rod "bearing" wasn't getting oiled and it only took about 15 seconds for everything to heat up and seize from aluminium getting smeared over the moving surfaces. If your engine is cutting out, it could possibly be seizing if some of the moving parts are jamming up when hot.

You could try getting a carb rebuild kit either on eBay (search for stihl + fs120 + carb + kit) or from Garden Hire & Spares Ltd in the UK (see link at end of article).


Nick Mifsud profile image

Nick Mifsud 3 months ago

Hi Eug - an update:

After erratic behavior I ordered a new carb from eBay, popped it on and it started working almost immediately. After it stalled, I managed to start it again: success. (At this stage, new carb, plug and air filter).

Next day: back to square one.looked like it was going to start with choke on, choke off and nothing. Managed to get it going once briefly but that's it.

Since then stripped and reassembled, checked spark, fuel flow looks okay when priming.

Baffled...

Am I missing something really obvious?

Nick


eugbug profile image

eugbug 3 months ago from Ireland Author

Hi Nick, sounds really frustrating!

So you've replaced the carb, plug and air filter, isn't really much left to trouble shoot!

I wonder has the flywheel moved on the shaft which would screw up timing and cause the spark to happen at the wrong time? I've never removed a flywheel on a small engine like this or checked how they are fixed to the shaft, but presumably it's the same as on a lawn mower with a slotted key way on both components and a key to prevent relative movement. If the key has sheared, the flywheel may be held tightly enough by the nut to stay in the right position some of the time, but then move and cause problems. However for the engine to have started properly after you replaced the carb, it would have to have moved back to the correct angle. You would probably need a pullers to remove the flywheel though. The bolt/nut holding on a flywheel, mitre saw blade, circular saw blade etc always loosens in the direction that the blade/disk/wheel turns.

The only other things I can think of are an ignition coil module which is breaking down or maybe the gasket on the crankcase giving trouble. Crankcase compression is necessary for proper operation. (See the link at the start about how a two cycle engine works). Also check the lead that feeds into the spark plug boot is making a good connection. These aren't actually crimped/spot welded/soldered to the spring which pushes onto the spark plug. Instead there's just a spike on the spring which pushes into the end of the HT cable.


Nick Mifsud profile image

Nick Mifsud 3 months ago

Yep, first paragraph makes sense...the shaft had been rotating slightly relative to the the engine casing...

So that's next weekend's activity sorted...

Thanks, as ever, for the advice....


Eduardo 3 months ago

I have problems with the primer/fuel line(s) of a McCulloch whipper snipper and I was considering the replacement for an electric one, but after reading your very professional description of the fuel system in a two stroke engine and the cleaning of the carburetor, I will give it another go replacing the hoses, cleaning the filter and carby ; your article is -by far- the best I've read about a small two stroke engine in the web, thank you very much!

Eduardo


eugbug profile image

eugbug 3 months ago from Ireland Author

Thanks Eduardo! I wasn't familiar with the name "whipper snipper" and to Google it and it turns out that's what trimmers/strimmers are called in Australia! Anyway thanks for the comments. If you're only doing light trimming, an electric machine is perfectly adequate and there are electric versions available with powers up to 1000 watt. That's well over 1 horse power, and they take a 2mm line.


Mike 2 months ago

I've spent several days trying to get information on this type of carb via Google and YouTube and nothing has come close to how informative your article is. I realize that it was written a couple years ago and I don't often make online comments but I wanted to thank you to show my appreciation for the hard work and time you put into writing this. This has been the only information I found on how the gas actually flows through the carburetor and I really appreciate the image showing the numbering sequence. that's exactly what I was looking for in order to figure out what my trimmers issue was. The only thing I still do not know and probably the only thing I could even remotely suggest adding 2 this article, : should the outer gasket go above or below the pump/reed valve gasket? meaning if the primer bulb is the bottom of the carb then the red-duck valve then the diaphragm then the part of the carb with the spring and meter.... To simplify - the picture in which you number the sequence of gas flow: Should the (outer) gasket go directly on top of that part of the carb and then the pump/Reed valve gasket... Or should it be the pump/Reed valve gasket and then (outer) gasket on top? In the picture with the gas flow numbers - on the left, the pump gasket and what I'm calling the outer gasket referring to the 2 tabs at the bottom. It would be greatly appreciated if you could reply or if anyone else knows the answer. I understand it's been a while since this was posted so thank you or any others in advance

Mike


Mike 2 months ago

Just to further clarify the above question in the picture of the pump/reed valve gasket you'll notice that there are 2 tabs at the bottom of this - each tab is a separate or in my case now a separate gasket. I have the same carb as shown, which has the 2 pin holes to help align everything, but when those 2 gaskets which are shown together in the picture are separated, one could be applied on the top of the other and still line up. Leaving me with the question of why didn't I pay attention to what one goes on the other.

Thanks again, and side note - with your info and while waiting over the weekend for my new carb I was able to get my little 2 stroke scooter running enough to get me to the corner store and take the dog for a run..... with a zip lock bag primer bulb and a plastic tape over hole pump gasket


eugbug profile image

eugbug 2 months ago from Ireland Author

Hi Mike, thanks for the appreciation!

If you look at the photo where I'm marking the fuel lines with the Tippex marker, it gives an idea of the assembly sequence (but you have to look at the other photos too to work everything out). I take your point that an assembly photo (something like an exploded parts diagram) would be useful. Anyway this is the sequence:

1: The bulb goes at the bottom

2: On top of that the primer bulb

3: Next the black plastic part that the bulb fits into

4: Followed by the diaphragm,

5: Next the aluminum part holding the spring/meter valve

6: The gasket

7: The pump reed valve piece (6 and 7 are stuck together in the photo above)

8: The carburetor section with the venturi which bolts onto the engine block

I never noticed the part with the reed valves is two separate sections (stuck together in my case, and looking at photos, I can see the tabs from the two pieces). If the pieces are swapped, the tabs still wouldn't line up. However, the gasket seems to make contact with the part of the carburetor I numbered, followed by the pum/reed valve section.

I don't know why the pieces are separate, presumably the gasket needs to be thick to fill imperfections in the machined surfaces, but the reed valves and pump have to be thin to sit flat on the ports and be flexible enough to flap up and down, plus the pump has to be thin to bulge in and out easily.

It would probably be a good idea to give the photos numbers, so you've given me some work to do this afternoon!


eugbug profile image

eugbug 2 months ago from Ireland Author

I've added a note in the text about the two parts stuck together. If you zoom in on the photo (zooming is awkward on HubPages. You need to left click to zoom, then right click, click view image from the menu, then left click again) you can see that the gasket section makes contact with the numbered part of the carburetor. I don't remember mixing them up, and I'm always particular about remembering assembly sequences (don't have a good memory, but a camera is a good substitute!)


Mike 2 months ago

You're right about the pictures that's always the best way to reassemble. Thank you and after a lot of online research you are definitely right about the gaskets touching the centerpiece in which you number and then the diaphragm low read valve above

Thanks again and for anyone looking to buy a new gasket set what you want to search for its walbro wyl series carb

rebuild kit

on Amazon for about 7 Bucks comes with everything from air filter gasket to primer bulb also includes the metering pin


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eugbug 2 months ago from Ireland Author

Yes, carburetor kits seems to be readily available for the trimmer in the photos above (well at least they look similar, so you can only buy and try). Search for "K20-WYJ Walbro repair kit" and you should get plenty of hits on eBay and Amazon. The websites listed at the end of the article also supply this kit.


Mike 2 months ago

I'm sorry I ment to say that in my case I needed to put another gasket on top of the diaphragm and the pump/reed with the aluminum section in the middle

Thanks again and I really appreciate an author who actually reads and responds to the comments. Often being the best part of reading blog posts on line


eugbug profile image

eugbug 2 months ago from Ireland Author

Thanks Mike. Possibly I have a gasket also on top of the diaphragm on my trimmer, so I must check this out. The kits have 6 parts so do you mean the diaphragm and pump section are both sandwiched between a top and bottom gasket?


Paul 5 weeks ago

GOOD ARTICLE , WELL DONE.

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    Eugene Brennan (eugbug)311 Followers
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    Eugene is a qualified control/instrumentation engineer Bsc(Eng) and has worked as a developer of electronics and software for SCADA systems



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