Adjusting air and fuel on the Stihl Chainsaw

Stihl air and fuel adjustment instructions

Adjusting Air and Fuel On The Stihl Chainsaw

Adjusting air and fuel on the Stihl Chainsaw is a fairly easy job. The fuel and air mixture in any gasoline-powered engine is regulated by the carburetor, and the carburetor in a Stihl chainsaw is pre factory-adjusted to provide the best performance. It goes out of adjustment quite quick after you have used the chainsaw for a while, tuning it up should be part of a regular routine maintenance. You’ll find three adjustment screws for the carburetor, usually located under the air filter cover. Your chainsaw typically has one of two types of carburetors that Stihl manufactures. You must first determine which type your chainsaw has, then you must follow a slightly different procedure to adjust each type of carburetor.

 

Fuel And Air Diagram Of A Stihl Carburetor Adjustment
Remove the cover off the air filter by turning the knob counterclockwise and lifting it off. Next remove the air filter and carefully 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.
Remove the cover off the muffler by unscrewing the screws that hold it with a Phillips type screwdriver. Remove the spark arrestor screen from behind the muffler and clean it with a small brush or 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.

What Type Of Carburetor On The Chainsaw?

Adjustment and Tuning Of A Stihl Carburetor DiagramDetermine the carburetor type before adjusting the high- and low-speed screws. A full strip down and assembly manual can be found in the carburetor manuals section of this website. Next, 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.

Useful Tools To Have Before You Start

Compressed air or soapy water
Phillips or crossdrive screwdriver
Small soft brush or toothbrush
Flat-head screwdriver
Never try to 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.
Only back the chainsaw idle screw off enough to make the chain stop turning. The chainsaw is dangerous if the chain stihl turns while it’s idling.
You can read more and find a complete Stihl carburetor service, repair and disassembly manual in the manuals section of the website, where you can view online images or download a full PDF manual to save or print off for workshop use.

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