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Honda String Trimmer Has No Power (8 Things to Check)

You’re not getting the power you’re used to when using your string trimmer. Keep reading to find out what can cause the engine to not run at full throttle.

A Honda string trimmer loses power due to a clogged 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.

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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.

8 Reasons a Honda String Trimmer Has No Power

Old Gasoline

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 Honda 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.

Because ethanol is harmful to a Honda small engine, it’s best to purchase fresh gasoline with a minimum octane rating of 87 and a maximum ethanol content of 10%.

  • 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 Honda at regular intervals.

If you are unsure if you’ll be able to consume it, 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 Honda string trimmer here.

SOLUTION: Drain the old fuel remaining in your string trimmer. Fill a Honda 4-cycle engine with a mixture of straight gas and 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.

Plugged Air Filter

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 Honda 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 or replace the Honda air filter if it is damaged or very dirty.

Clean a Honda 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 filter oil. Squeeze excess oil from the filter. (Do not oil pre-filters)
  • Reinstall the filter.
  • Reattach the air filter cover.

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

Dirty Spark Plug

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 Honda trimmer and to rule it out as being part of the problem.

Next, check the electrode gap. This must be gapped to the Honda’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.

Clogged Fuel Filter

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.

How to replace a Honda string trimmer fuel filter:

  • Wipe around the fuel cap to remove dirt, and then remove it.
  • Empty the fuel tank into a clean fuel container.
  • Set the trimmer on a flat surface.
  • Pull the fuel filter out of the tank using a clean bent wire to hook the fuel line. Needle nose pliers may also work.
  • Securely holding the fuel line, securely grab the filter and pull it out of the fuel line.
  • Install a new fuel filter at the end of the fuel line.
  • Place the filter back inside the fuel tank.
  • Fill with fresh gas
  • Place the fuel cap onto the fuel tank.

Clogged Fuel Line

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.

Dirty Carburetor

A carburetor is used on a Honda string trimmer to regulate the amount of gas mixed with air to create 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 Honda carburetor.

Plugged Fuel Tank Vent

The Honda fuel tank vents through a small plastic part attached to the end of a fuel line coming out of the fuel tank.

When this part becomes plugged, 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 Honda 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.

Plugged Spark Arrestor

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 carbon restricting airflow. You may experience a loss of power.

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.

When to Have a Mechanic Repair Your Honda 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 Honda 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 Honda trimmer that’s on its last leg.

You have the consider 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 Honda string trimmer.