Why Your Brush Cutter Won't Start, and What to Do About It
What to Check When Your Brush Cutter Doesn't Start
You go out to start your brush cutter, weed whacker, or string trimmer and it won't start. If you've tried a few times and it still won't start, and you smell gasoline, you've probably flooded it. Wait about 10 minutes before you try again to give the gasoline time to evaporate.
If it still doesn't start, I'd like to tell you the procedure we use here on our farm when this happens and how we solve the problem with our Stihl FS85 brush cutter. Although we have a Stihl, most brush cutters and string trimmers will be similar to work with, use these steps as guidelines in conjunction with your manual.
The first thing my husband does is swear. This step is completely optional, but it seems to help him.
The problem may be:
- The spark plug
- The air filter
- The fuel
- The carburetor
- The solenoid
Let's look at each of these steps, to pinpoint the problem and find the solution to get you back to work cutting grass and weeds.
Checking the Spark Plug
Remove the spark plug and if there's gas on it, that's good, it means the gas is getting through.
The spark plug may be getting coked up if your engine isn't running at its best. Also if your air filter is dirty, this will affect your spark plug.
If your spark plug is dirty use a fine emery paper to remove any deposits around the electrodes. If you have a gapping tool that measures the distance, in a spark plug, it should be 0.02 inches (0.5mm). If the gap is too large use a pair of pliers to minimize the space. Other brands of brush cutters may have a different recommended gap, so check your manual.
The spark plug should be good for roughly 100 hours of use so if yours is getting close to those hours; this is an easy and inexpensive fix.
Checking the Air Filter
The next step should be to check your air filter. It's easy to think that cutting grass and weeds shouldn't clog it, but if you've been working in a dry and dusty environment, it could be the problem. Tap out the dust and if yours is felt you can wash it. Leave it to dry completely before returning it to the machine.
This is something you'll want to check frequently if your cutting is kicking up a lot of dust. By cleaning the air filter, this will stop that coughing and sputtering noise you may be experiencing with your machine. By periodically checking the air filter, you'll be helping your machine work to its best.
We live near sand dunes and have strong winds, so dust particles are a common problem for us.
Carburetor Problems in a Brush Cutter
One of the last things to check will be the carburetor; this could likely be the cause if your brush cutter has been left standing for some time as the gasoline may have clogged it up. As the gasoline begins to evaporate, a sticky residue is left behind.
Here on our farm, the carburetor is our main problem as the gasoline where we live is combined with alcohol and is full of grit. Although we use a funnel with a fine filter, small debris gets through and can clog up the jets in the carburetor.
The quality of fuel you use is important, and a higher octane (89 or above) is suggested by most manufacturers of brush cutters. When the octane is lower, you'll get a pinging, and your machine will run less efficiently.
If you don't know the recommended octane level for your brush cutter, check your manual that came with your string trimmer. If you don't have it any longer, most manufacturers offer this online, and you can download it. It will tell you not only the recommended octane of gasoline to use but also the correct gas to oil mixture. Your manual will also show you where the high and low-speed adjustments are (if any), some less expensive models don't have this adjustment. These adjustments will allow you to alter the amount of fuel/air going in so your machine will be working at its best. Instructions are also shown in the video below.
If your carburetor is dirty, wipe it over but don't use a carburetor cleaner, as the circuits may be damaged by this spray. You are best to use an ultrasonic cleaner.
Note: I have included a video below where the man is using a carburetor cleaner, however, I have spoken with a Stihl repair center, and they discourage using aerosol cleaners on the carburetor.
Changing the Carburetor on a Brush Cutter
If your brush cutter won't start, and you have had it for about two years, then, in our experience, the problem is most likely your carburetor. Learn from our experience here; my husband has tried cleaning it and adjusting it as a way of saving money. This may work in the short-term but, this problem is going to reoccur. So now, when my husband knows the carburetor is on its way out, he gets a new one. Our nearest parts center is 40 miles away, so we try and keep a spare carburetor. The time spent trying to repair the part just isn't worth it.
Buy the part and replace it yourself. Once you can do this simple repair, you'll become more confident and begin to realize that you can repair virtually everything on your brush cutter. Not only does this save you money, but it also allows you to solve the problem quickly and keep your homestead or farm maintained and minimizes any downtime.
Solenoid on Brush Cutter
Recently we had to change the solenoid on our brush cutter. You may be wondering how my husband knew it was the problem and not something else. To understand this, you need to know what a solenoid does. It simply changes an electrical current into mechanical energy. If you have changed your spark plug and you still aren't getting a spark, it's the solenoid that needs replacing. We bought the part; my husband replaced it following the instruction regarding the size of the gap needed and a few minutes later the machine was working.
Not only was it running again, but it was also almost like he had a new machine. Although we have had the brush cutter for eight years, this was the first time he had to change the solenoid.
Replacing the Line on a String Trimmer and Brush Cutter
Now that you have got your machine working again, you'll need to wind your string on. If you're serious about your cutting and maintaining your machines, rewinding your string is something you'll need to learn.
Here on our farm, we don't mess about with those small packs seen hanging in the garden center or nursery; we buy a large roll which works out much cheaper.
Brush Cutter, Weed Whacker, String Trimmer
Although they are basically the same type of cutters, they are known by different names. The brush cutter is a more robust version of a string trimmer. On some models, it will come with a blade, chainsaw or flailing chain attachment to use on scrubland or small coppices. The motor capacity will also be greater as will the weight of the machine.
Some models will also have different styles of support systems. For example, ours has a crossbody strap, others have a backpack and some, which are lighter weight, have no support.
Some of the names you may have heard are:
- String trimmer
- Brush cutter
- Strimmer (UK)
- Bush Cutter
- Weed Whacker
- Weed Eater
Learn to Troubleshoot
If your brush cutter or string trimmer won't start you need to act quickly. Here on our farm, our Stihl brush cutter is a crucial piece of equipment, and we can't afford to have it not working. Therefore, my husband has learned to troubleshoot quickly.
We know that whether we're clearing a large piece of land or simply cleaning up an area around the lawn, being without the right equipment at the right time can make the job more difficult.
It isn't a case of putting it down and hoping it will work the next time it's picked up; the problem needs sorting immediately so we can carry on with the work on our farm.
Are You Using Poor Quality Gasoline?
If it has been some time since you started your machine the first thing to check is that the fuel lines aren't blocked. Where we live, our gasoline is rather poor quality, and many times, although we use a filter in our gasoline funnel, small bits of debris find their way into our gasoline tank. This doesn't only cause problems with the hoses, but also the tubes.
Before we leave the subject of gasoline, if you have finished using it for the season, make sure you leave the tank empty, gas can bung up, and you don't want to have to solve the problem come spring when you need to use it again. This is an easy way to prevent future problems.
String Trimmer Keeps Cutting Out
If you can get your brush cutter going, but it keeps cutting out and stalling, you might be wondering why this is occurring. This too can be caused by problems with your carburetor. Follow the guidelines above in the video and in your manual to find the perfect balance of air/gas for your machine.
When using the brush cutter, try and ensure you vary between low and high revs as using it only on low is likely to cause carbon problems and get coked up. You don't have to run it with the throttle wide open; they are made to be working with a load.
Do you do your own repairs on your brush cutter or string trimmer?
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
Is there a way of checking if the spark plug is sparking?
Yes, there is. Take the spark plug out but leave it connected to the cable. You have to ground this by placing it on a metal part of the machine. Ideally on top of the cylinder head. DO NOT put it anywhere near the gas tank!
Set the machine to start and pull the cord. You should see a spark. If it is 'white/blue' that is good. If it is looking yellow/orange it's getting weak.
Changing the spark plug is an easy fix. Also, check to see if the gap is correct by using a gapping tool. For a Stihl brush cutter, the correct gap is 0.02". Check your manual or online for your specific measurement.Helpful 2
When I tried to start my two stroke brush cutter, it has no sparks and fuel started coming out of the exhaust pipe. What do I do?
The first thing is to check your spark plug. In the article I mention things to look for. Clean it, and check the gap is correct. Or buy a new spark plug. Changing the spark plug is an easy fix. The gas coming out is because it isn't being burned.
If you change the spark plug and it doesn't rectify the problem, it's likely your solenoid.Helpful 16
I used a 2-stroke line trimmer without oil now the machine won't start. What's the problem and how do I start it again?
I am sorry to be the one to give you the bad news but it's very likely you've seized up the engine. My advice is to go and buy another machine.Helpful 13
My Stihl fs160 keeps dropping power in the process of running. What could be the problem?
Here are a few things to check:
It could be the exhaust outlet is blocked with carbon deposits.
Remove exhaust and check and scrape away carbon if necessary.
It may also be dirt in the carburetor. Remove the carburetor and clean. Clean or change gaskets and diaphragm if necessary.
Check your fuel lines are clear and clean.
Check your fuel tank filter is clean.Helpful 8
When I tried to start the Weed Eater, it blows gasoline out of the carburetor, why is that?
It sounds like you have a blockage. Check the carburetor for debris and if that doesn't solve it, check your fuel lines.Helpful 8
© 2017 Mary Wickison