Skip to Content

10 Reasons a Troy-Bilt String Trimmer Loses Power

When you begin experiencing a lack of power from the engine, the performance of your string trimmer suffers. Your trimmer is no longer able to efficiently trim the grass to give your lawn a well-manicured appearance.

A Troy-Bilt string trimmer loses power due to a plugged air filter, dirty spark plug, plugged fuel filter, clogged fuel line, dirty carburetor, bad fuel tank vent, plugged spark arrestor, or old fuel.

Before performing repairs, let the engine cool down and wait for all parts to stop moving. Remove the spark plug wire for safety.

Troy-Bilt string trimmer loses power

This post may include affiliate links. Purchases made through these links may provide a commission for us, at no extra cost to you. As an Amazon Associate, we earn from qualifying purchases.

Follow all safety instructions provided in your equipment operator’s manual prior to 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 a Troy-Bilt String Trimmer Has No Power

1. Old Gasoline Causes a Troy-Bilt String Trimmer to Lose Power

When it comes to a string trimmer that’s losing power, the main culprit is often old gas. Gas can begin to break down and become less effective as soon as 30 days after purchase.

Most gas includes the alternative fuel, ethanol, to help make it more environmentally friendly. This is because ethanol is made from plants.

Ethanol may be better for the environment, but it’s not good for the small engine on a Troy-Bilt trimmer. This is because it naturally attracts moisture from the air to the fuel system.

The water and ethanol mixture can leave behind varnish causing fuel restrictions and component failures. This mixture will also separate from gas over time and run extremely hot through the engine potentially causing damage.

Because ethanol is harmful to a Troy-Bilt small engine, it’s best to purchase fresh gasoline with a minimum octane rating of 89 and a maximum ethanol content of 10%.

  • 2-cycle engines require gas to be mixed with a premium 2-cycle engine oil like this oil from Kawasaki at a ratio of 40:1. (Mix 40 parts gas to 1 part oil).
  • 4-cycle engines require straight gas. Do not mix with oil.

Never use fuels with higher ethanol contents like fuels sold as E15, E30, and E85 fuel. These have ethanol contents up to 15%, 30%, and 85% respectively.

Consume fuel within 30 days. It can be difficult to estimate how much fuel you will go through especially if you don’t use your Troy-Bilt at regular intervals.

If you are unsure, add a fuel stabilizer to the fuel so it lasts a little longer before it breaks down. Read more about the right fuel to use in a Troy-Bilt string trimmer here.

SOLUTION: Drain the old fuel remaining in your string trimmer. Fill a Troy-Bilt 2-cycle engine with a 40:1 gas and oil mixture. Fill a Troy-Bilt 4-cycle engine with straight gas. Add a fuel stabilizer like Sea Foam Motor Treatment.

This product will not only stabilize the fuel, but it will also reduce moisture and clean the fuel system.

Start the string trimmer and allow it to run to work the fresh fuel and fuel stabilizer mixture through the fuel system.

2. Plugged Air Filter Causes a Troy-Bilt String Trimmer to Lose Power

An air filter allows the engine to get clean air while keeping dirt out. When the filter isn’t cleaned or replaced regularly, it can become plugged restricting the amount of air allowed to pass through the filter.

Without sufficient air, a Troy-Bilt string trimmer will run sluggishly and lose power.

I recommend replacing the air filter once a year and cleaning it several times throughout the year. You will have to clean and replace it more often if you use your trimmer in very dusty conditions or more than the average homeowner.

You may be tempted to run your string trimmer with the plugged air filter removed to get it running well. Do not do this even if it’s only for a few minutes to finish a task.

Doing so can contaminate the engine with dirt and debris causing permanent engine wear and damage.

SOLUTION: Clean the Troy-Bilt air filter or replace the filter if it is damaged or very dirty.

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 and allow it to air dry.
  • Once dry, lightly saturate the filter with clean SAE 30 engine oil. Squeeze excess oil from the filter.
  • Reinstall the filter.
  • Reattach the air filter cover.

Consult your operator’s manual for instructions when cleaning other types of air filters.

3. Dirty Spark Plug Causes a Troy-Bilt String Trimmer to Lose Power

Excessive carbon buildup on the spark plug can result in intermittent spark and a loss of power. Remove the spark plug and ensure it is in good condition.

SOLUTION: If it is very dark in color or is damaged, replace it with a new spark plug.

You can try cleaning a lightly dirty plug using a small wire brush. I prefer to replace the plug since it is a vital component of a well-running Troy-Bilt trimmer and to rule it out as being part of the problem.

Next, check the electrode gap. This must be gapped to the Troy-Bilt’s specification. The spark plug wire must be securely attached as well. A loose spark plug wire or an incorrect gap can cause a loss of power.

4. Plugged Fuel Filter Causes a Troy-Bilt String Trimmer to Lose Power

The fuel filter is a small cylinder-shaped part located inside the fuel tank. It is attached to the fuel line.

Its purpose is to strain fuel as it passes through the filter to keep dirt and other contaminants from entering the fuel system causing wear on the engine.

The fuel filter should be changed annually to keep it in good condition. When it becomes plugged, the amount of fuel that is able to pass through it is lessened.

Reduced fuel to the engine can cause the engine to lose power.

SOLUTION: Replace a fuel filter that is plugged and won’t allow a good flow of fuel to pass through it.

Check the fuel tank to make sure the fuel is of good quality and it’s not contaminated with dirt and debris. If the fuel is very dirty or old, replace it with fresh clean fuel.

5. Clogged Fuel Line Causes a Troy-Bilt String Trimmer to Lose Power

The fuel line can become restricted with gummy deposits left behind from using old fuel. A clog in the fuel line can narrow the area fuel can pass through restricting the amount of fuel moving through the fuel line.

SOLUTION: Inspect the fuel line looking for any clogs preventing fuel flow. Replace a fuel line that is clogged, kinked, or has developed cracks from age.

6. Dirty Carburetor Causes a Troy-Bilt String Trimmer to Lose Power

A carburetor is used on a Troy-Bilt string trimmer to regulate the amount of gas mixed with air for combustion. Old fuel can gum the carburetor and cause the small internal components to stick so it no longer functions as designed.

SOLUTION: If you are a little mechanical you should be able to handle cleaning your carburetor. Clean the carburetor by taking it apart and using carburetor cleaner to clean it.

If the carburetor does not function after being cleaned, you may need to rebuild it (if a rebuild kit is available) or replace it with a new Troy-Bilt carburetor.

7. Plugged Fuel Tank Vent Causes a Troy-Bilt String Trimmer to Lose Power

The Troy-Bilt fuel tank vents through the fuel cap. When the cap becomes faulty and no longer allows air to pass through the cap, the fuel tank will form a vacuum when it is no longer able to vent.

This vacuum prevents a good flow of fuel from getting to the carburetor.

To determine whether the fuel tank vent is bad, place the string timmer on a flat-level surface and loosen the fuel cap to allow air to enter the fuel tank. Be careful not to allow gas to spill out of the tank.

If the engine begins to run better and no longer bogs down with the throttle lever depressed, you may have a fuel tank vent problem.

To further confirm the problem, tighten the fuel cap and run your Troy-Bilt trimmer. If after running for a while, it begins to bog down and only runs better after loosening the fuel cap, the problem most likely is the result of a bad cap.

SOLUTION: The fuel tank vent can be found off of a fuel line coming out of the fuel tank on some models and in the fuel tank cap on others. A bad fuel tank vent must be replaced.

8. Plugged Spark Arrestor Causes a Troy-Bilt String Trimmer to Lose Power

A spark arrestor is a small screen attached to the muffler to keep hot exhaust material from shooting out of the muffler causing injury or starting a fire.

This small screen can become plugged with soot restricting airflow. You may experience a loss of power as a result.

SOLUTION: Disconnect the spark plug wire. Remove the engine cover and the engine exhaust cover. Carefully remove the spark arrestor screen. Clean it with a small metal brush.

If the screen isn’t able to be sufficiently cleaned or you find it is damaged or has a hole in it, the screen must be replaced with a new one.

9. Carburetor Adjustment on a Troy-Bilt String Trimmer

The carburetor may need to be adjusted to change the RPMs at idle speed and at full throttle. It may be causing the engine to run lean or rich causing the trimmer to run rough.

There are adjustment screws on the carburetor to make these adjustments, however, you most likely need a special tool to make these adjustments.

If none of the items listed above have solved your problem, I recommend having a mechanic at your local Troy-Bilt service center troubleshoot the trimmer and make any necessary carburetor adjustments. Over-adjusting the carburetor can permanently damage the engine.

10. Carbon Buildup in the Exhaust Port Causes a Troy-Bilt String Trimmer to Lose Power

The exhaust port located behind the muffler can develop carbon deposits that can cause your Troy-Bilt string trimmer running problem.

This area should be checked and cleaned when you are experiencing a loss of power that hasn’t been fixed by the items above.

SOLUTION: To avoid damage to the trimmer, I highly recommend having an experienced mechanic clean the exhaust port and muffler. If you don’t know what you’re doing, you can easily damage the trimmer beyond repair.

If you choose to attempt to clean it, first disconnect the spark plug wire and make sure the engine and muffler are cool so you don’t burn yourself.

Remove the engine cover, the muffler, and the heat shield. Adjust the piston until it covers the port opening. This will keep carbon from falling into the cylinder.

Use a plastic scraper to remove the carbon buildup around the exhaust port. DO NOT use a metal tool.

DO NOT scratch the piston or the cylinder during this process. Reinstall the items in the reverse order you removed them.

When to Have a Mechanic Repair Your Troy-Bilt String Trimmer?

If you’ve gone through the list above and it didn’t solve your loss of power issue or you don’t feel comfortable performing any of the repairs, it is time to consider consulting an experienced small engine mechanic to have the engine checked.

You may have a good small engine repair shop near you that has been recommended by a neighbor or friend. You can also find one by visiting the Troy-Bilt dealer locator page.

I prefer to go to the dealership for manufacturer-trained support when I run into a significant issue. They have the proper equipment to perform necessary testing. They also carry OEM parts and can take care of any warranty items.

When visiting the repair shop, keep in mind the labor rate for the mechanic to diagnose your problem. There is typically a flat rate charge to diagnose the problem and then add labor and parts fees in addition to the fee to make the repairs.

Paying a diagnostic fee, parts, and a labor bill may not be sensible if you are running an old inexpensive Troy-Bilt trimmer that’s on its last leg.

You have the weigh the reliability, quality, and age of your current string trimmer against the cost of the repair. You may be better off investing in a new Troy-Bilt string trimmer.