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My Lawn Mower Won't Start? Basic Troubleshooting Tips for Small Engines

Eugene has a keen interest in DIY and gardening. Over a 30 year period he has also become self taught in garden power tool maintenance.

Lawn Mower Won't Start After Winter

For an engine to startup, it basically requires two things: fuel and a spark. If you aren't getting a spark at the plug or fuel isn't getting through to the engine (known as fuel starvation), the machine will never startup. Bad compression can also lead to difficult starting. After storage during winter, seals, pumps and valves in the carburettor can become gummed up with varnish deposits if you leave fuel in the tank. During the summer, dust and dirt can block the fuel system or clog filters.

While the information here applies to lawnmower engines, it is equally valid for other small engines used on yard equipment, such as portable generators, pumps, cultivators, snow blowers, compactors (wackers), cement mixers etc.

Snow blowers use 4 stroke engines just like lawn mowers

Snow blowers use 4 stroke engines just like lawn mowers

WARNING!!! Before You Start Any Mower Troubleshooting...

  • When working on a mower, remember that gasoline/petrol is flammable. Remove all sources of ignition such as naked flames, stoves, sparks, cigarettes or other hot objects in the vicinity when working on the tank or fuel lines.
  • Disconnect the spark lead if you have to remove any clumps of grass jammed under the deck and need to tilt the mower.
  • Check the manual to determine how your mower should be tipped for deck cleaning, oil changes or blade removal. Sometimes manufacturers recommend keeping the carburetor upwards, pointing skywards. Alternatively the plug may need to be uppermost with the handles tipped back onto the ground (you'll need a heavy weight such as a concrete block to keep the mower in this position). Don't turn the mower so that the carburetor and air filter face downwards as engine oil can foul the carb and filter, leading to difficulty in starting.
  • Drain the tank if you estimate the fuel level will reach the cap. The cap has a vent and fuel can trickle out through this.
  • Turn off the fuel tap if fitted. Then run the engine until it cuts out if the mower needs to be placed on its side or plug side up. The float bowl on some engines has an overflow and fuel can trickle out this vent. Also the float may not operate properly when the engine isn't horizontal, causing the carburetor to overflow into the intake manifold of the engine. If fuel leaks onto the outside of a hot engine, it can potentially start a fire. If the mower only needs to be raised a little to unclog the deck, you don't need to turn turn off fuel or drain the tank, but always disconnect the plug lead.
Remove the spark lead if you need to clean under the deck or turn the blade. Ideally remove the plug

Remove the spark lead if you need to clean under the deck or turn the blade. Ideally remove the plug

Check the manual for the recommended way to tilt the mower. Sometimes manufacturers recommend placing a mower on its side with the carburetor pointing upwards.....

Check the manual for the recommended way to tilt the mower. Sometimes manufacturers recommend placing a mower on its side with the carburetor pointing upwards.....

......alternatively the mower can be placed back on its handles with a heavy weight such as a concrete block to keep it in place.

......alternatively the mower can be placed back on its handles with a heavy weight such as a concrete block to keep it in place.

Checking Lawn Mower Oil

Check the oil level is ok before starting. Move the mower to a level surface, remove the dip stick and wipe clean. Replace it and remove again. Check the oil is between the high and low marks before starting. Top up if necessary. Oil should be changed after every 25 to 50 hours of run time as advised in your engine manual. An oil change is reasonable easy to do. You can find more details in my guide How to Change Lawn Mower Oil

Checking the oil in a lawn mower. Oil level should be between the high and low marks on the dipstick

Checking the oil in a lawn mower. Oil level should be between the high and low marks on the dipstick

How Do You Start a Small Engine?

  1. Set the throttle to high revs or the choke position. If the engine has a manual choke turn it on
  2. Press the primer button (if fitted) about 8 times
  3. Pull the starter rope quickly, but try not to yank it too hard
  4. Allow the engine to reach top speed before using. If the engine has a manual choke, turn it off after about 5 seconds
  5. Don't turn a manual choke back on again if you need to start a hot engine

A Checklist to Get Your Mower Started

Tip 

1

Use fresh gas. Don't use old gasoline which can cause difficult starting. Make sure there is enough fuel in the gas tank and check the vent in the tank cap is unblocked

2

Check the spark lead is firmly attached to the plug, and the plug is tightly screwed in. Try replacing spark plug with a new one

3

Make sure the "dead man's handle" control on the mower is held fully against the mower handle while starting.

4

Turn on choke if a manual choke fitted. Don't turn on the choke if the engine has been running in the last 5 minutes or so

5

Make sure primer bulb is pressed about 5 times (if fitted). If the mower runs out of gas during cutting, it will need to be primed again

6

Check the air filter isn't dirty. Wash and dry foam type air filter (see below for details), or replace dirty paper filter

7

Check the cable connecting the "dead man's handle" on the frame to the engine is not damaged or snapped

8

Check the carburettor is tightly screwed or bolted to the engine

9

Make sure there is no water lodged at the bottom of the gas tank

10

If the starter cord is hard to pull, check there are no clumps of grass clippings clogging the underside of the deck. These can jam the blade. Disconnect the spark lead before attempting to move the blade to remove clippings!

11

Some newer push mowers have starter motors and batteries. The battery voltage should be over 12 volts for the engine to start.

More Advanced Troubleshooting

If you still can't get your mower started, checkout my advanced troubleshooting guide which covers more in-depth problem solving of issues with fuel flow and starvation, the carburetor, ignition (electrical) system, choke, valves and compression.

How to Fix a Lawn Mower That Won't Start

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

Question: How do I check for a spark on a lawn mower engine?

Answer: Follow the procedure mentioned in my article:

You may need an assistant if the plug can't be seen while pulling the cord.

1. Find a shaded location.

2. Remove the plug.

3. Attach the lead back onto the plug.

4. Hold the plug threads against the engine block. (An assistant could hold it with a plastic clothes peg)

5. Don't touch the lead or the plug!!

6. Pull the starter cord.

Question: If I put starting fluid in the carburetor and it still does not start, can you pass over the carburetor in troubleshooting as a none starting problem?

Answer: You don't have to troubleshoot in sequence. If you want you can check the spark plug, connections, air filter, etc. first. The important thing is to check or change one thing at a time and see the results.

Question: I replaced the magnetic pick up in my mower, but there is still no spark. What can I check next?

Answer: Replace the spark plug, check the ground of the pickup or that the ignition coil is making contact with the engine block. Also, check the spark lead and make sure the kill switch isn't shorting out the primary when the throttle is set to the run position.

© 2015 Eugene Brennan

Comments

smithy1199 on June 22, 2020:

Thank you, that worked.

Eugene Brennan (author) from Ireland on June 19, 2020:

I presume you mean you placed it on its side? It's possible that oil ran out of the engine into the carburetor and fouled the air filter. Remove the air filter housing and check whether this has happened. You can wash sponge filters in detergent, squeeze dry in a cloth and add a teaspoon of motor oil and massage it through the foam. Paper filters may need to be replaced. It's possible either that petrol flooded the carburetor, so allowing the mower to sit for a while for it to drain and evaporate before attempting to start could help.

smithy1199 on June 19, 2020:

I place my mower on it's side, it starts but for seconds only, what should I do to repair it? Thanks in advance

Eugene Brennan (author) from Ireland on October 18, 2019:

Hi David,

It could be several things including a battery that wasn't fully charged when you bought it so starting took a big chunk of charge out of it. The charging dynamo/alternator may not be doing its job, the regulator/charging circuit (if it's a separate unit from the dynamo/alternator/dynastarter) may be faulty, fuses could be blown etc. I'm out of my depth on ride on mowers and the charging systems/starter motors. If it's brand new, hopefully it came with a warranty, so it's best not to meddle with it. The battery voltage should be 13 volt or so for a fully charged battery, so if it's less than 12 volt there's some sort of charging issue.

David Addison on October 18, 2019:

just bought a new ride on mower got it started ran for a few minutes,turned it of tried to re-start nothing no lights on or anything, Any ideas please

Eugene Brennan (author) from Ireland on August 27, 2019:

Overfilling shouldn'treally prevent it from starting. Fuel flow is regulated by a device called a float bowl, located under the tank. This pretty much acts like a toilet cistern, the reservoir keeping fuel at a constant level, irrespective of how much fuel is in the tank. If the inlet valve from the tank isn't working properly in it though, maybe fuel could overflow into the carburetor, flooding it Try removing fuel and leave the mower to sit for a while for any fuel in the carburetor to evaporate. Not sure how you'll remove excess fuel form the tank. Sometimes I use a thoroughly washed out pump from a handwash bottle that produces a jet and squirt fuel into a container (don't use a spray type version!).

Jackie on August 27, 2019:

I overfilled my petrol lawnmower with petrol and now it won’t start !!!

Eugene Brennan (author) from Ireland on May 18, 2019:

Possibly, but you need to consult the manual that came with the mower or contact the store for further details. New mowers are also normally sold without engine oil (so it doesn't leak out if a boxed mower ends up upside down during transit) so you will more than likely have to add that also. Check the dipstick.

Loa Knight on May 17, 2019:

starter cord has limited pull and when I looked underneath saw theres a metal pole on each side preventing full rotation of the blade itself. does that need to be removed 1st? (brand new mower)

JON on October 05, 2018:

THANK YOU !

Larry Rankin from Oklahoma on June 04, 2015:

Very useful! It's good to have an article like this to reference when my small engines won't start.