Poor Performance, STIHL String Trimmer Lags Behind

You won’t have enough muscle to finish the job with a string trimmer. So that you may achieve the best performance from your trimmer, I have compiled a list of things to inspect.

When the gasoline, air, and spark of a STIHL strimmer are inadequate, the engine runs roughly and stalls.

The fuel may be stale, the fuel filter may be clogged, the fuel line may be clogged or punctured, the carburetor may be dirty, the fuel tank’s vent may be clogged, the air filter may be clogged, the spark arrestor screen may be clogged, or the spark plugs may be unclean.

For further information on how to operate a STIHL safely, please refer to the user manual. Pull the wire from the spark plug and let the engine cool down completely before attempting any repairs.

String Strimmer
String Strimmer

8 Causes of Roughness and Slowdown in Your STIHL String Trimmer

A STIHL String Trimmer Has a Rough Time Running When the Fuel Is Old or Corrupt.

If your trimmer starts acting sluggish and jerky, you may want to examine the quality of the gasoline it is receiving.

After only 30 days, fuel can start to deteriorate and become useless. Most gasoline contains ethanol, which is a liquid that draws moisture and causes problems in a fuel system.

Old gas will leave varnish and sticky coatings from this moisture-ethanol mixture. As a result, fuel flow is restricted and the carburetor may break down.

To get the most out of your trimmer, you need to consider both the type of fuel you use and the rate at which it is spent. By carefully selecting and maintaining the fuel, you can lessen the likelihood of difficulties caused by using gas that is getting on in years.

Blending 50 parts gasoline to 1 part 2-cycle engine oil is recommended for STIHL string trimmers. When deciding what kind of gas to buy for your STIHL string trimmer, keep in mind the following:

  • You should choose 89-octane or higher unleaded petrol with no more than 10% ethanol added.
  • Before adding it to the fuel tank, mix gasoline and 2-cycle engine oil at a ratio of 50:1. If you want to know more about the gasoline used in STIHL String Trimmers, click here. Make use of a fuel blend containing both oil and gas.
  • Use up your gas within the next 30 days.
  • If you won’t be using the fuel within 30 days, you can extend its shelf life by adding a fuel stabilizer.
  • Keep gasoline in a cool, dry place away from flammable materials.

FIX: You should drain the gasoline tank of any stale gas. In a gas container, combine fifty parts unleaded gasoline with one part engine oil designed for two-cycle engines. To prevent the fuel from deteriorating and to clean the fuel system, you should use a fuel additive such as Sea Foam Motor Treatment.

Pour the mash into the gas tank. Turn on the string trimmer and let it run to distribute the fresh gasoline.

Putting new fuel in your string trimmer could make a noticeable difference in its performance right away. Try the next thing on the list if that doesn’t work and keep going down the list until you discover something that does.

Difficult Operation of a STIHL String Trimmer Caused by a Clogged Fuel Filter

In addition to checking the fuel filter, make sure you have new gasoline combined with 2-cycle engine oil at a ratio of 50:1.

Inside the fuel tank is a little cylinder-shaped component called the fuel filter. This filter should be changed once a year as part of your regular maintenance.

Without frequent replacement, the filter might become clogged with the debris it is supposed to trap before it enters the fuel delivery system. Blocking the filter prevents fuel from reaching the carburetor.

FIX: Substitue the clog in the STIHL fuel filter.

  • Arrange the trimmer in a horizontal position.
  • Remove the gasoline cap and wipe the area around it.
  • A fuel filter needs to be removed from the tank. The fuel line can be successfully connected with a clean, bent wire. Perhaps a lengthy pair of needle-nose pliers will allow you to get at it.
  • When you have a firm grip on the fuel line, you may safely remove the filter from the fuel line.
  • Replace the old fuel filter with a new one.

A STIHL String Trimmer with a Clogged Fuel Line

Look into the gasoline line to see if there is any obstruction or kink that is preventing fuel from flowing freely. Fuel that is filthy or old fuel that has left sticky deposits might cause blockages.

Be on the lookout for a clog, but also for a puncture in the line, which could let air to enter the fuel line and cause the trimmer to bog down.

If you discover a clog, kink, puncture, or leak in a STIHL fuel line, the solution is to install a whole new fuel line. A STIHL retailer is the place to go to get your hands on some genuine OEM parts.

The filter should be reinstalled within the tank such that it faces the back and is near the tank’s base.

A STIHL String Trimmer with a Clogged Carburetor Gives It a Rough Ride

The carburetor controls the flow of fuel into the engine and the amount of air that is sucked in to create combustion, allowing the STIHL to start and run.

It’s possible that the string trimmer’s performance will degrade if the gas-to-air mixture is off. Carburetor passages can become blocked and the little parts that make it up can stay.

Due to this, the STIHL carburetor may not provide the necessary gasoline to the engine.

The carburetor could only need to be cleaned in order to function again. In the event that cleaning the carburetor does not improve its performance, you may be forced to either repair it (if your carburetor is compatible with rebuild kits) or replace it.

Old fuel can corrode carburetors, a typical problem. Using new fuel will save wear and tear on the carburetor.

Using a non-ethanol fuel, such as pre-mixed MotoMix fuel, will prevent damage to the carburetor caused by ethanol.

A STIHL String Trimmer with a Dirty Spark Plug

The trimmer may misfire and run poorly if the spark plug is filthy. A filthy spark plug isn’t the only thing that can make it run rough; an improper electrode gap and a slack wire can do the same thing.

FIX: Take out the spark plug with a socket wrench. Verify the state of it. In the event that you notice the tip of the spark plug is very black, the porcelain is fractured, or the electrode is scorched, you should replace the spark plug.

It’s up to you whether you want to clean the spark plug using a wire brush if it’s in good working order but unclean, or if you want to just buy a new one.

Since it’s a cheap part that has such a big impact on the string trimmer’s efficiency, I usually just buy a new one and install it.

A String Trimmer from STIHL with a Blocked Fuel Tank Vent.

The gasoline tank’s vent should also be checked. To allow the gasoline tank on a STIHL string trimmer to vent, this little item must be installed.

The fuel tank’s internal pressure is maintained at atmospheric pressure by allowing air to flow in and out.

If the fuel tank vent is blocked or doesn’t work properly, the fuel tank will create a vacuum, reducing the amount of fuel reaching the carburetor. Not having enough gas in the tank can make the trimmer sputter.

Removing the gasoline cap and letting air into the tank is a quick and easy way to check for a blocked fuel tank vent. Kick on the string trimmer and let it go. To avoid leaking gas from the tank, be mindful and maintain the string trimmer on a flat surface.

Whether the engine of your STIHL trimmer runs smoothly without stalling or running rough, try tightening the gasoline cap and seeing if the problem persists; if so, the fuel tank vent is likely the cause.

FIX: If, after restoring the fuel cap, your trimmer continues to act up and operate roughly, the fuel tank vent should be replaced.

Uneven Performance Due to Clogged Air Filter in STIHL String Trimmer

In order to keep the engine clean, the air filter is installed. Filtering contaminated air before it reaches the carburetor throat, the filter keeps the engine running smoothly.

If the air filter is not routinely inspected, cleaned, and replaced, it can get so clogged with dirt that not enough air can pass through it.

If there isn’t enough air, the motor will sputter and stall. Maintaining clean air is crucial to preventing engine overheating and malfunction.

FIX: If the air filter is in good condition, check its condition and clean it as described below. There needs to be a new filter installed if the old one is severely clogged, covered with fuel, or otherwise damaged. Lower the choke to prevent debris from entering the carburetor.

STIHL string trimmer air filter cleaning procedures:

  • Lower the choke to prevent debris from entering the carburetor.
  • Taking off the air filter’s cover.
  • Clean up the area around the filter.
  • Take out the filter and clean the vents.
  • The dirt can be dislodged from the filter by tapping it against your palm. If you need more air, get a compressor. It is recommended to get a new filter if the old one is too unclean or worn out.
  • Put on a new air filter.
  • Put the filter back in its housing.

A Rough Run Can Be Caused By A Clogged Spark Arrestor On A STIHL String Trimmer

A STIHL string trimmer has a spark arrestor screen added for your protection. It prevents burns or fires from occurring if hot exhaust material were to suddenly shoot out of the muffler.

It’s important to inspect and clean this screen. If soot builds up, it restricts airflow, slowing the engine’s performance.

Fix: Let the muffler cool down before cleaning the spark arrestor. Detach the wire from the spark plug.

Take apart the spark arrestor and clean the screen with a small wire brush to get rid of any residue from the exhaust system that may have accumulated there. Any screen that has been punctured or is otherwise damaged must be replaced.

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