A finely tuned Stihl chainsaw will run and cut without any problems and make the job easier. Keeping the saw running at optimal performance will, at some point, require manually adjusting the carburettor. Properly adjusted carburettors will help protect the engine and ensure the Stihl saw has a long life. Tuning the carburettor is easy and should be performed whenever you notice poor engine performance, a chain that spins when throttled or an engine that dies when idling.
Remove the air filter from the saw and clean out all of the debris and dirt inside the filter. Replace the filter if it is dirty or old.
Use an Allen wrench to unscrew the muffler's cover. Take off the cover and pull out the spark arresting screen located inside the muffler. Clean the spark arrester or replace if damaged.
Fill the saw with fresh gas with a 50:1 gas-oil ratio. Add fresh bar oil to the bar oil tank.
Start the saw and let it idle to warm up. Find the three carburettor screws. On Stihls, these screws are found above the clutch plate on the same side as the bar.
Locate the H screw and throttle the saw. With the saw at full speed, turn the H screw counterclockwise until the engine produces a loud, high-pitched sound. Turn the screw back one half to three quarters of a turn clockwise off the maximum engine speed.
Locate the L screw and turn the screw clockwise until the screw stops. Turn back the screw one-quarter position again.
Turn the L screw counterclockwise until the engine makes a heavy bubbling sound. Twist it back one quarter turn clockwise.
Re-tune the idle speed by repeating the idle tuning section steps.
The chain should never spin when the chainsaw is not throttled.
Tuning the high speed above the recommended factory settings can cause major engine failure and permanent damage.