How to Adjust the Air and Fuel on a Stihl Chainsaw

Smoking or faltering usually means your saw's carburetor needs adjusting.

Smoking or faltering usually means your saw's carburetor needs adjusting.

The fuel/air mixture in any gasoline-powered engine is regulated by the carburetor, and the carburetor in a Stihl chainsaw is factory-adjusted to provide the best performance. It goes out of adjustment as you use the saw, and tuning it up should be part of routine maintenance. You'll find three adjustment screws for the carburetor, usually located under the air filter cover. Your saw has one of two types of carburetors that Stihl manufactures. You must first determine which type your saw has, then you must follow a slightly different procedure to adjust each type.


Take the cover off the air filter by turning the knob counterclockwise and lifting it off. Remove the air filter and clean it with compressed air or by washing it with soapy water. If you wash it, wait for it to dry before reinstalling it and adjusting the carburetor.


Take the cover off the muffler by unscrewing the screws that hold it with a Phillips screwdriver. Remove the spark arrestor screen from behind the muffler and clean it with an old toothbrush. Reinstall it and replace the muffler cover.


Look for the carburetor adjustment screws either near the air filter or under the spark plug. There are three of them, marked "H," "L" and "I" or "LA," depending on the model. They are the high-speed, low-speed and idle adjustments respectively.


Determine the carburetor type before adjusting the high- and low-speed screws. To do this, turn the "L" screw clockwise as far as it will go, using a flat-head screwdriver, then turn it counterclockwise as far as it will go. If it turns more than one complete revolution, it's a type A carburetor, and if it turns less than one revolution, it's a type B carburetor.


Return a type A carburetor to its factory setting by turning the "H" screw counterclockwise until it stops, turning the "L" screw clockwise until it is seated, then backing it off one full turn. Adjust a type B carburetor by following the same procedure, but instead of backing the "L" screw off one turn, back it off only 1/4 turn.


Adjust the idle screw after starting the saw and letting it warm up for about five minutes. Turn the "I"or "LA" screw clockwise until the chain starts to turn, then back it off 1/4 turn.

Things You Will Need

  • Compressed air or soapy water
  • Phillips screwdriver
  • Toothbrush
  • Flat-head screwdriver


  • Never adjust the carburetor when the air filter is dirty. A dirty filter restricts air flow.
  • If your saw doesn't run properly after making these adjustments, the carburetor may need to be fine-tuned by a professional service person, using a tachometer.


  • Always back the idle screw off enough to make the chain stop turning. The saw is dangerous if the chain turns while it's idling.

Photo Credits

  • Jupiterimages/ Images
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