Stihl chainsaws have carburettor settings that allow you to adjust the fuel and air mixture in the carburettor. This innovative feature lets you set the idle speed and the low and high speed RPM. At some point you will need to reset the carburettor on your chainsaw. This should be done if the chain moves when idling, dies when idling or is sluggish when throttled. You should always clean the air filter and muffler screen before setting a Stihl chainsaw carburettor.
Start the saw and let the engine warm up for a few minutes. Locate the three small screws on the bar side of the saw, near the chain brake handle.
Use the small screwdriver to adjust the LA screw, or idle screw. This screw is usually the bottom screw if the lettering has worn off.
Turn the screw all the way in clockwise or until the chain starts spinning. Twist the screw back one-quarter turn.
Use the screwdriver to adjust the L screw, or low-speed screw. Turn the screw in clockwise all the way or until the engine makes a surging sound. This is the lean setting for the gas. Turn the screw back one-quarter turn and remember the setting of this screw.
Turn the screw back counterclockwise until the engine makes a heavy bubbling sound. Twist the screw back clockwise one-quarter of a turn. Remember the position for the rich mixture.
Fine-tune the L screw by adjusting it between the rich and lean settings found in the previous steps. Listen for the cleanest and clearest sound from the engine.
Depress the throttle and use the screwdriver to set the H screw, or high-speed screw.
Turn the screw in clockwise until the engine makes a high-pitched whine, then back off the throttle immediately. Turn the screw back one-quarter turn and remember this lean setting.
Throttle the saw again and turn the screw counterclockwise until the engine slows down or gets sluggish. Twist the screw back clockwise one-quarter turn and remember this setting for the rich mixture.
Fine-tune the screw by holding down the throttle and adjusting the screw in between the rich and lean settings. Listen for the cleanest and strongest sound from the engine.
Readjust the low-speed and idle screws after finishing the high-speed screw.
Never adjust the carburettor when the engine is cold. Never set the high-speed screw above the maximum factory RPM recommendations. Use a tachometer if you have any doubt about the proper sounds your engine should make.
Setting the high-speed screw above the RPM limit will overheat and ruin your engine very quickly.