Your string trimmer is acting up and won’t stay running. I’ve put together a list of items to troubleshoot to get you back to your lawn care tasks.
A Troy-Bilt string trimmer starts, stalls, and then dies when it isn’t getting sufficient fuel, air, and spark.
This may be due to a dirty carburetor, clogged fuel filter, clogged fuel line, bad spark plug, faulty ignition coil, plugged air filter or plugged spark arrestor.
Before performing repairs, always follow the safety precautions found in your Troy-Bilt operator’s manual. This includes removing the spark plug wire and waiting for all parts to stop moving.
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Follow all safety instructions provided in your equipment operator’s manual before diagnosing, repairing, or operating. Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.
10 Reasons Your Troy-Bilt String Trimmer Starts Then Dies
1. Incorrect Choke Setting
The choke is used to restrict airflow and allow the fuel mixture to run rich to start a cold engine. Once the engine warms, the choke must be in the open/off position to continue to run.
When the choke isn’t adjusted after the engine warms up, it will begin to sputter and die because it isn’t getting the fuel-to-air ratio required to keep it running.
If your Troy-Bilt string trimmer starts and dies right away, check the position of the choke lever. If the choke lever isn’t in the correct position, the trimmer will die.
SOLUTION: Make sure it is placed in the off position once the engine is warm.
2. Plugged Air Filter
Just like your Troy-Bilt engine can die from a lack of air when the choke is left on, it can stall and die when enough clean air isn’t able to flow past a plugged air filter.
Your Troy-Bilt string trimmer requires an air filter to prevent dirt and debris from getting sucked into the engine causing wear. It must be kept in good condition to keep dirt out while allowing air to pass through it.
I recommend replacing the air filter at the beginning of every lawn care season. Then check and clean the filter several times throughout the season.
Never run your string trimmer without an air filter, even if it’s just for a short period so you can finish your task. Doing so can compromise the engine and void any warranty remaining on your trimmer.
SOLUTION: Clean the air filter. Purchase a new air filter if your filter is extremely dirty or damaged. I have included instructions to clean a foam air filter. For other types of filters, consult your operator’s manual.
Clean a Troy-Bilt FOAM string trimmer air filter:
- Remove the air filter cover and air filter.
- Clean the foam air filter using water and mild detergent.
- Rinse the filter until the water runs clear, squeeze to remove water, and allow it to air dry.
- Once dry, lightly saturate the filter with clean SAE 30 engine oil. Squeeze excess oil from the filter. (Do not apply oil to a foam pre-cleaner).
- Reinstall the filter.
- Reattach the air filter cover.
3. Old or Bad Fuel
Running old fuel through your Troy-Bilt string trimmer can cause it to stall and run sluggishly. Most gasoline contains ethanol, a corn-based fuel that is added to make fuel more environmentally friendly.
While better for the environment, it is not good for the small engine used on your Troy-Bilt. The gas and ethanol mixture can begin to break down as soon as 30 days after purchase.
Ethanol and the water it attracts are corrosive to the trimmer. It leaves behind a varnish that reduces the amount of fuel getting to the engine.
Because of the negative effects ethanol has on small engines, avoid running gasoline with high amounts of ethanol. Use unleaded gasoline with a minimum 89-octane rating and a maximum 10% ethanol content in your Troy-Bilt string trimmer.
A fuel without ethanol is always best, but it is the more expensive fuel choice.
2-cycle and 4-cycle Troy-Bilt string trimmers have different fuel requirements.
- 2-cycle engines require a gas and oil mixture at a rate of 40:1. An unleaded gas is mixed with a premium 2-cycle engine oil like this oil by Briggs & Stratton. 3.2 oz. of oil is mixed with 1 gallon of gas.
- 4-cycle engines require straight gas. Do not mix with oil.
Only use fresh gasoline in your string trimmer. You can find more information about choosing the right gas and oil for your Troy-Bilt string trimmer here.
SOLUTION: Drain old fuel from the string trimmer. Fill with fresh fuel with a fuel additive like Sea Foam Motor Treatment mixed in to make the fuel stable, reduce moisture, and clean the fuel system.
Start the trimmer and allow it to run for 5-10 minutes to allow all of the fuel to work its way through the fuel system.
4. Plugged Fuel Filter
The fuel filter helps keep the fuel system clean and free of dirt and debris that may get into the fuel tank. You will find the fuel filter on your Troy-Bilt string trimmer attached to the fuel line inside the fuel tank.
A fuel filter should be replaced annually and possibly more often if you happen to be running dirty fuel.
When it isn’t changed, the filter can become so plugged that a sufficient amount of fuel isn’t able to pass through the filter causing your Troy-Bilt trimmer to run sluggishly or quit running.
SOLUTION: Replace the fuel filter. If the fuel is dirty, replace it with fresh fuel.
Replace a Troy-Bilt fuel filter:
- Wipe around the fuel cap to remove dirt and debris so they don’t fall into the tank.
- Remove the cap.
- Pull the fuel filter out of the fuel tank. A clean bent wire or needle nose pliers work well to retrieve the filter.
- Once the filter is out of the tank, remove it from the fuel line.
- Attach the new fuel filter by inserting it into the fuel line.
- Place the fuel filter back inside the fuel tank.
- Install the fuel cap.
5. Clogged Fuel Lines
Old fuel can leave behind deposits that stick inside the fuel lines. This narrows the passageway and the amount of fuel that flows through the line.
SOLUTION: When this happens, remove the fuel line and install a new fuel line of the same diameter and width. You will need to replace the fuel line if you find it is dry, cracked, or kinked.
6. Plugged Fuel Tank Vent
The fuel tank on a Troy-Bilt string trimmer must have a vent to allow air to pass into the fuel tank as fuel is consumed. When this vent is plugged vacuum forms in the tank keeping fuel from getting to the carburetor.
If you are not getting fuel to the carburetor and you have verified you are running a good fuel filter and you don’t have a clog in the fuel line, you may have a plugged fuel tank vent.
SOLUTION: You can check the pressure of the tank with a pressure gauge to make sure there isn’t a vacuum buildup. However, most people don’t have a fuel line pressure gauge on hand.
Follow the instructions below to determine whether the fuel tank is venting properly without a pressure gauge.
Perform this simple test to help identify a bad fuel tank vent.
- Loosen the fuel cap to allow air into the tank and start the trimmer. Don’t allow gas to spill out of the fuel tank.
- Start the engine and allow it to run. If it runs fine and doesn’t begin to sputter or stall, you may have a vent problem.
- Try to replicate the issue to further confirm the vent is the problem.
- Tighten the fuel cap and run the string trimmer. If it begins to run sluggish or shuts down and doesn’t start again until you loosen the fuel cap, replace the fuel tank vent.
The fuel tank vent on most Troy-Bilt trimmers is built into the fuel cap.
7. Dirty Carburetor
The carburetor mixes the correct proportion of air and fuel required for your Troy-Bilt string trimmer to run. The passageways can become clogged and the small components can fail to function correctly.
This can cause an insufficient amount of fuel mixed with air resulting in a rough running string trimmer that may just quit.
SOLUTION: You may be able to clean your carburetor to get it working again. You may end up having to rebuild it (if rebuild kits are available for your Troy-Bilt carburetor) or replace the carburetor if cleaning doesn’t help.
Before replacing a carburetor, I recommend comparing the cost of the carburetor and labor expense to the cost of a new Troy-Bilt string trimmer.
Depending on the model, cost, and age of your string trimmer, you may be better off purchasing a new trimmer.
8. Dirty Spark Plug
The spark plug will become dirty over time with a buildup of carbon. This can cause the plug to misfire having intermittent starting problems.
Other items to look for are cracked porcelain, worn electrodes, a loose spark plug wire, and an incorrect spark plug gap. These items can also cause a running issue with your Troy-Bilt.
SOLUTION: You can attempt to clean a dirty spark plug with a wire brush and reuse it. I prefer to replace it especially if it’s the reason your trimmer is dying.
It is an inexpensive part and one of the primary items responsible keep your string trimmer running at its best.
Make sure your spark plug is gapped to the manufacturer’s specification and the spark plug wire (boot) is securely attached.
9. Bad Ignition Coil
The winding on the ignition coil can separate and short out. When this happens, the spark plug won’t get the voltage required to create a spark. This will cause your Troy-Bilt to die after it’s been running.
SOLUTION: Identify a bad ignition coil using an ohmmeter to check for a break in continuity. Replace the ignition coil if you find a break.
10. Plugged Spark Arrestor
You will find a small metal screen attached to the bottom of the muffler. This is to prevent hot exhaust material from shooting out of the trimmer causing injury or starting a fire.
This small spark arrestor screen will become plugged with a carbon buildup that will affect how the engine runs.
SOLUTION: Disconnect the spark plug wire. Remove the muffler cover. Carefully remove the spark arrestor cover and screen. Inspect the spark plug for damage.
If it is in overall good condition, clean it with a wire brush and reinstall it. However, if it is damaged or has a hole in it, you must replace it with a new spark arrestor screen.
Contact your local Troy-Bilt service center if you are having trouble locating the spark arrestor screen or if you are continuing to experience problems with your Troy-Bilt string trimmer.
You may require a carburetor adjustment that should be performed by an authorized service center.