Here is an instruction on how to simply tune up your STIHL FS38 45 55 trimmers.

Spark Plug

Firstly, you need to pull the spark plug off. Loosen the spark plug and pull the plug out. The manufacturers tell you that you need to put the spark plug in there until the bit tilts your finger tight. So the gasket actually is making contact finger tight and then you take your spark plug wrench to turn that another half a turn until it is snug. Now you need to put the spark boot back on and push it down to the zip.

Air Filter

Then you are supposed to get the carburetor off. The reason why you need to take the carburetor off to do part of a tune-up is to check or to replace your air filter and fuel filter.
You need to get your air filter cover off as well as the air filter itself. Check the condition of the air filter and replace it if necessary. Then you can see two nuts in there, remove the nuts and the air filter house.
Before we actually pull the carburetor off, we need to disconnect two fuel lines and the throttle cable.

Fuel Filter

Now after you put the carb off, you need to pull the whole grommet out of the fuel tank by using pliers to check if your fuel line is good. Put the fuel filter off and you can blow it out with some air and suck through it to see if it is actually restricted or not. Replacing your fuel line if necessary. Do not forget to reconnect the fuel lines and the throttle cable onto the carburetor until you put the air filter housing and the air filter on.

Throttle Cable

If the throttle waver does not go down all the way to the stop when you are fully squeezing the trigger, that means you need to adjust it to make your trimmer runs well. There is a little screw for cable adjustment on some STIHL trimmers while there is a little slot in the handle for throttle adjustment on others. You can use a flat screwdriver to screw in the adjustment screw or stick it into the slot and push in until the throttle waver reaches the stop.

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