String Trimmer from STIHL Slows Down and Loses Power (8 Reasons)

Lack of power from your string trimmer makes it difficult to complete the task.

Because of a gasoline limitation brought on by used fuel, a dirty carburetor, a dirty fuel line, or a blocked fuel tank vent; a limitation of airflow brought on air filter clogged or a filthy spark causing a lack of spark, or a spark arrestor screen plug, a STIHL string trimmer bogs down and loses power.

Keep yourself safe and adhere to all the STIHL operator’s manual safety instructions. If you are unaware of how to carry out repair procedures, speak with a qualified mechanic.

Eight causes of a STIHL string trimmer’s lack of power

A STIHL String Trimmer Loses Power Due to Old Gas

When your STIHL string trimmer starts to stagnate and loses power, check the fuel quality. This generally occurs because of old gas.

The ethanol used in gasoline will eventually evaporate n addition to the moisture it draws, leaving beneath sticky varnish residues. Fuel constraints as a result of this will make the engine sluggish.

Use new 89 octane minimum, maximum ethanol content in the fuel concentration of 10% because ethanol is bad for a STIHL string trimmer’s small engine and performance.

Mix at a 50:1 ratio with 2-cycle engine oil. (1 part oil to 50 parts gas). Never use gasoline with an ethanol content greater than 10%, such as E15 or E85. These have ethanol content of up to 15% and 85%, respectively.

When choosing and keeping fuel for your STIHL string trimmer, remember the following advice:

  • Buy new fuel: Invest in fuel you can probably use inside of 30 days.
  • Use a fuel stabilizer: To extend the lifespan of your fuel, add a fuel stabilizer. In many 2-cycle lubricants, fuel stabilizers are present. From
  • 30 days to 2 years, according to the oil’s manufacturer, the fuel stability may be maintained.
  • Choose the proper gas: Use gas with an octane rating of at least 87 and a maximum of 10% ethanol.
  • Use a gas-to-oil ratio of 50:1: 1 part premium 2-cycle engine oil must be combined with 50 parts gasoline.
  • Fuel should be kept dry and from flammable materials items.

Check out STIHL String Trimmers Use This Type of Gas and Oil Fuel Mix for additional information on selecting the proper fuel for your trimmer.

WORKAROUND: Remove any residual old fuel from using your string trimmer replace it with a brand-new 50:1 gas-to-oil blend.

Include a fuel stabilizer that further aids to minimize moisture and fuel system cleaning, such as Sea Foam Motor Treatment.

Run the string trimmer after starting it. You must permit the mixture of fresh gasoline and sea foam to circulate throughout the system.

After replacing with new gasoline, you might notice that your STIHL trimmer is starting to operate stronger and is not anymore losing strength. If not, work your way via way of this list to continue troubleshooting the issue.

Loss of Power in a STIHL String Trimmer Due to Plugged Air Filter

Use of a STIHL string trimmer requires the air filter. It prevents dirt and other debris from entering air intake, as well as harming the engine.

A trimmer’s air filter protects it, but if it isn’t kept clean and in good shape, it can also become a problem.

If the air filter is not changed, dirt can accumulate and clog it, preventing the engine from receiving the air it needs to operate at its peak. The engine could become less powerful due to a lack of air.

I advise changing the STIHL air filter once a year and then periodically inspecting and cleaning it across the entire year. When working in extremely dusty conditions, you might require more replacements frequently.

The air filter should be examined and cleaned if necessary. It must be changed if it is severely soiled or destroyed.

Cleaning the air filter on a STIHL string trimmer

  • To prevent dirt from entering the carburetor throat, close the choke by turning the knob.
    the air filter cover must be removed.
  • Clear the area around the air filter of debris.
  • Take the air filter off.
  • To make dirt fall from the filter, tap the filter against the palm of your hand. If necessary, use a compressor for air. Replace the filter with a new one if it is seriously clogged or damaged.
  • Put the air filter in place.
  • the filter housing back on.

An unpowered STIHL string trimmer is caused by a dirty spark plug.

An erratic spark could be caused by a dirty spark plug. As a result, your string trimmer can lose power.

WORKAROUND: Take out the spark plug to inspect it. It is necessary to replace the spark plug tip if it is extremely dark in color, worn, or broken.

You can use a small wire brush to clean the spark plug tip if it is clean and in good shape.

Check the electrode gap next. According to the manufacturer’s instructions, t has to be gapped. Additionally, the spark plug wire needs to be firmly fastened. A loss of energy could be brought on by a loose spark plug wire or an improper gap.

Loss of energy in a STIHL String Trimmer Due to Plugged Fuel Filter

The fuel filter can be found inside the fuel tank. To prevent dirt from entering the gasoline system, this cylinder-shaped component is fastened to the fuel line. The fuel filter is sometimes referred to by STIHL as the pickup body.

To keep the fuel filter in good condition, it should be replaced every year. The filter may clog up with dirt if it isn’t changed frequently.

This might prevent the engine from receiving enough fuel, which would make it run slowly and become weak.

Replace a fuel filter if it is preventing fuel from reaching the fuel line. Make sure the filter is positioned near the lowest point of gasoline tank when you reinstall it.

inspect the fuel tank.

Loss of energy in a STIHL String Trimmer Due to Clogged Fuel Line

The fuel line is another area to look for a fuel restriction. Deposits that are gooey could obstruct fuel flow through the fuel line could be left behind by old fuel. Another possibility is that you have an opening that is allowing air into the fuel system.

Your STIHL may bog down and operate rough due to a fuel limitation or an excessive amount of air being introduced via way of the fuel system.

Check the fuel line for any obstructions obstructing gasoline flow. Replace any fuel lines that are cracked, kinked, or clogged.

An unclean carburetor reduces the power of a STIHL

On a gas-powered STIHL string trimmer, a carburetor is necessary to control the volume of gas and air combined to produce combustion. Your carburetor may no longer operate properly if the little parts become clogged with old fuel and stick.

Solution: You must be capable of clean your carburetor if you are a bit mechanical. Take the carburetor apart, then clean it with carburetor cleanser.

while disassembling the carburetor, take pictures with your phone pictures of it so you can look back on them when you reassemble it.

If after cleaning the carburetor it still doesn’t work, you might must be rebuilt (if a rebuild kit is available) or get an updated carburetor.

Causes of a Clogged Fuel Tank Vent Failure of a STIHL String Trimmer

Air must be capable enter and exit the fuel tank so that it can escape. This is made possible through a fuel tank vent, which you will discover.

A clogged fuel tank vent prevents air from passing by way of it to balance the the gasoline tank’s internal pressure with the outside air.

As a result of the fuel tank creating a void once it can’t properly vent, the STIHL string trimmer will sputter and lose force. Fuel cannot flow to the carburetor due to this vacuum.

Loosen the fuel cap to let air into the tank and check the vent on your fuel tank to see if it is blocked. Following that, if your string trimmer starts to operate more efficiently, there’s a significant likelihood the fuel tank vent is blocked.

Whether you allow the STIHL to run with the cap tightened to see if you feel a decrease of power and then loosen the cap to experience a better-performing trimmer, you can try to reproduce the issue to further validate it.

To prevent spilling petrol from the fuel tank, exercise caution and keep the trimmer level. You must inspect and replace the fuel tank vent if you can reproduce the problem.

REMEDY: Change a clogged fuel tank vent.

A STIHL string trimmer loses power due to a plugged

The STIHL muffler’s spark arrestor is a tiny metal screen that keeps hot exhaust from escaping and igniting a fire.

Your STIHL string trimmer can lose power and stop turning at its maximum RPMs when this tiny screen gets clogged with soot.

Put the trimmer’s blade in the off position as a solution. Take the spark plug wire off. Hold off until the muffler cools. Remove the spark arrestor screen with care. Utilize an iron brush to clean it.

Replace the screen with a new spark arrestor screen if it cannot be cleaned thoroughly, if you discover it to be damaged, or if it has a gaping hole.

When Should a STIHL String Trimmer Be Repaired by a Mechanic?

Consider consulting a skilled small engine mechanic if you’ve examined the list above, and it didn’t resolve your power loss problem or if you don’t feel confident doing any of the fixes.

A neighbor or acquaintance may have recommended an excellent repair business for small engines in your area. Additionally, you can locate one by going to the STIHL dealer locator page.

When I have a severe problem, I prefer to go to a STIHL dealership to get repairs made. Factory-trained mechanics are a requirement for STIHL dealerships. As a result, STIHL is not sold in big-box stores.

STIHL dealers have the specialized equipment needed to conduct testing. Additionally, I can be sure any warranty will function has been done and that the repair was made with OEM components.

Consider the labor cost hen the mechanic can determine your issue when you visit a repair shop. Typically, there is a flat rate price to identify the issue, followed by labor and part costs to finish the repairs.

If you have an outdated, cheap STIHL trimmer that is towards the end of its useful life, the cost of the diagnostic test, components, and labor costs might not make sense.

You must balance the expense of the repair against the string trimmer’s age, quality, and dependability. You could do better to spend money on a brand-new STIHL string trimmer.