How to Troubleshoot a Stihl FS55

Check the felt element inside your Stihl trimmer's air filter. If you notice a significant loss of power when you press the throttle, it may mean the air filter is dirty. Press in the tab on the air filter cover and lift it off. The filter cover is located on the left-hand side of the trimmer, in front of the gas cap.

Remove the felt element by hand from the air filter. Blow it out with canned air (or replace it with a new one) and then place it back into place and replace the filter cover.

Remove the spark plug boot by hand and then use a spark plug wrench to remove the old spark plug. Screw a new spark plug in by hand and then tighten it with the spark plug wrench. Replace the spark plug boot.

Adjust the speed screws on your Stihl trimmer. These three screws are located on the back of the carburetor. Insert a screwdriver into the "H" high-speed screw at the top left and then turn it three-quarters of a turn to the left. Place the screwdriver into the "L" speed screw at the top right and then turn it clockwise until it stops, and then turn it back one-and-a-half turns. Twist the idle speed screw, located beneath the high and low screws, to either the left or right until the trimmer's head does not spin while the engine runs.