8 Most Common Stihl FS94R Problems and How To Fix Them

Having a grass trimmer at home is essential for maintaining a gorgeous lawn. It helps ease trim back weeds, tall grasses, and unnecessary foliage. Likewise, STIHL FS94R cares for lawn areas you can’t reach with a lawn mower.

This professional, gasoline-powered shaft trimmer delivers the best power-to-weight ratios in its class. Specifically, the STIHL FS94R combines reliable performance with variable speed control.

Despite being a highly effective landscaping tool, it sometimes encounters problems that make the simple task challenging. We will point out some STIHL FS94R problems and mention their solutions.

Stihl FS94R Parts

Before we discuss the problems with the STIHL FS94R weed Wacker, it is essential to know the parts of the STIHL FS94R.

8 Common Stihl FS94R Problems and How to Fix?

STIHL FS94R Problems and Its Solutions

Does your STIHL trimmer stop despite following the correct procedures for using it? Then, the problem may be with the engine, fuel, spark, or air circulation in the combustion chamber. No matter what, there is a way to fix all these problems.

Let’s look into the STIHL FS94R trimmer problems and their solution.

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Problem 1: Engine Doesn’t Fire

When you try to start the STIHL trimmer, the engine usually doesn’t start and leaves a gasoline smell. You possibly followed the proper guideline to start the STIHL trimmer but failed.

Possible Reasons – The STIHL FS94R carburettor may be flooded.

How to Fix It?

Wait for 10 minutes before you try to start up your STIHL trimmer again. Follow the steps below to start the STIHL FS94R.

  • Make sure to set the ON/OFF switch to ON.
  • Push the priming button two or three times.
  • Close the choke knob and pull the starting cord.
  • After two or three pulls, the engine is supposed to sputter.
  • If you open the choke knob and pull it again, the engine is supposed to start.
  • Be sure to press the throttle to restart the engine before it dies.

Problem 2: A Sputtering Engine

The engine sputters but won’t entirely start. It’s a sign of a lean fuel mixture in the combustion chamber. That means the engine is down on power, making it difficult to run at idle speed.

Possible Reasons – The air filter or spark arrestor may be clogged.

How to Fix It?

Locate the air filter behind a plastic cover on the side of the engine housing. And the screen attached to the muffler by a single screw is the spark arrestor. Follow the steps below to fix the clogged air filter or spark arrestor.

  • Pull off the plastic cover located on the side of the engine housing
  • Take out the filter using a screwdriver. Clean and replace it, if needed.
  • If the engine is still down on power, check the spark arrestor. You may either replace or clean the spark arrestor.
  • To access the spark arrestor, remove the muffler cover first.
  • Wait for the muffle to cool down.
  • Remove the screw and lift the spark-arresting screen.
  • Pull the spark arrestor out and clean it.
  • To clean the spark arrestor, immerse the spark-arresting screen overnight in a strong solvent. Use acetone or lacquer thinner.
  • If the spark-arresting screen is heavily carbonized or damaged, you must fit a new one. 
  • Refit the screen. Then, insert the screw and tighten it firmly.

Problem 3: Spark Plug Problems

The engine may be down on power because of spark plug problems. The spark plug is usually rated for 100 hours of use. If the spark plug needs to be repaired, it either won’t spark or weakly.

Possible Reasons – Possibly, it’s time for spark plug replacement. Or, a dirty air filter causes deposits to build up in the engine, which leads to fouled spark plug.

How to Fix It?

  • Inspect the spark plug to decide whether to clean or replace it.
  • If you decide to clean and reuse it, scrape off the deposits from the electrodes using an emery board.
  • Inspect the gas using a gapping tool. The gap should be 0.02 inches.
  • Adjust the gap using pliers, if necessary.
  • If the electrodes are severely eroded, you must install a new one.
  • Install a new suppressed spark plug that STIHL approves.

Problem 4: STIHL Trimmer Head Problems

The STIHL FS94R trimmer starts and runs, but the trimmer head doesn’t spin as it should. This is a common problem with trimmer heads.

Possible Reasons – Clogged trimmer head, clogged air filter or spark arrestor, lack of lubrication, and improper placement in the gearbox.

How to Fix It?

The first thing to do is to look over the equipment and check its overall condition. Then, check around the trimmer head to see if any fibrous plants and roots are twisted tightly. If any, you may have to cut them with a knife.

  • Start the trimmer to find out what the issue might be.
  • Let it warm up, and squeeze the trigger.
  • The engine may not be producing enough power to spin the head.
  • Or perhaps the spark arrestor or the air filter is blocked. If so, you need to replace both.
  • Remove the louvered cover from the intake port to access and remove the air filter. Or pull out the spark arrestor located behind the plate.
  • If the head rotates very slowly after squeezing the trigger, the problem may be in the gearbox. Remove the gearbox from the shaft.
  • Remove the bolt on the side and check that the grease in the gearbox has not dried up. If there is a lack of lubrication, the bearing might be gone and cause a lot of drag on the engine.
  • If the lubrication is still good, it may not be a bearing issue, but something is wrong with the head.
  • Spin the drive shaft to see if there is any drag from the clutch drum bearing near the engine. If it’s spinning, the drive shaft is just fine.
  • Now put the gearbox on the shaft to remove the head. Lock the drive shaft so you can spin the head off of the shaft.
  • Use a drill bit, a small screwdriver, or an Allen wrench and spin the head to remove it.
  • Check if the thrust plate and the washer are in the correct placement. The thrust plate must be placed first near the shaft and followed by the washer.
  • Finally, warm up the engine and start the trimmer again to see if it is spinning correctly.

Problem 5: Arcing

Arcing mainly happens if the adapter nut is missing or loosened. It could ignite combustible fumes. Working with a loose or missing nut in an explosive or easily combustible temperature can lead to an explosion. It can cause damage to property or severe injury.

Possible Reasons – Loosen or missing adapter nut.

How to Fix It?

  • Check that the spark plug is connected correctly. If not, secure the boot.

Problem 6: Loss of Engine Power

Along with making weird noises, there can be a noticeable loss of engine power at times.

Possible Reasons – Clogged air filter

How to Fix It?

You need to clean or replace the air filter. Follow the step below to clean the air filter.

  • Set the knob to the “g” position for the warm start.
  • Turn the screw counterclockwise until the filter cover is loose.
  • Remove the filter cover and clean the loose dirt from around the filter.
  • Hold the recess firmly in the filter housing and remove the filter.
  • Replace the filter if needed. Press the filter on your palm, or overdo it with compressed air. Do not wash the filter.

Problem 7: Fuel Problems

STIHL FS94R mostly requires an equal amount of oil or gas mixture to run. If you fail to add oil and gas mixture in the specified ratio, the engine can seize. Also, the trimmer shouldn’t be kept idle for an extended period with a full gas tank. It can cause fuel to clog the carburetor.

Possible Reasons – Improper ratio of oil and gas. Clogged STIHL FS94R carburetor.

How to Fix It?

You need to drain or clean the carburetor. However, it may be a strenuous job. Check the gas cap, if it is adequately tightened. If not, the fuel delivery system won’t work correctly. After solving the carburettor issue, take the STIHL FS94R to a technician.

Problem 8: Unnecessary High Loads

A trimmer run at high revs for the first three tank fillings can cause unnecessary high loads. The full-throttle offload happens during the break-in period.

Possible Reasons – When the trimmer runs at high revs during the break-in period.

How to Fix It?

A factory-new machine must not run at high, especially during the break-in period, to avoid unnecessary high loads. The frictional resistances in the engine may be greater during the break-in period.

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Final Thoughts

Now that you have learned how to fix the STIHL FS94R problems. Although STIHL recommends doing all the repairs and maintenance by STIHL dealers, it’s cost-efficient to do it yourself. So, find out the problems and fix them NOW!

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