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How to Adjust the Carb on a Stihl Trimmer

Updated April 17, 2017

The carburettor on a Stihl weed trimmer mixes the gasoline from the gas tank with oxygen before sending it to the engine cylinder to be ignited. The carburettor comes from the factory with the optimal carburettor settings, but as the engine ages, or if the carburettor is accidentally bumped, you will need to adjust it in order to get the engine running at the peak level. This procedure will take 10 minutes to complete.

Set the trimmer on a hard, level surface. Locate the carburettor on the right side of the trimmer directly below the air filter. There are three adjustment screws on the side of the carburettor; there is a stamping on the carburettor body marking each adjustment screw. The one marked "L" is the low speed adjustment, the "H" is the high-speed adjustment, and the "LA" is the low idle adjustment.

Gently turn the "H" screw clockwise until it seats with a flathead screwdriver, then turn counterclockwise one full turn. Gently turn the "L" screw clockwise until it seats with the flathead screwdriver, then turn counterclockwise one full turn.

Start the trimmer and turn the "LA" screw clockwise slowly until the engine stops, then turn counterclockwise one quarter of a turn. Advance the throttle from the SLOW position to the FAST position several times to ensure a smooth acceleration.

Things You'll Need

  • Flathead screwdriver
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About the Author

Based out of Orlando, Fla., Yvonne Grant has since 1997 done everything from designing and outlining company handbooks to preparing reports for the IRS. She maintains a popular interior design blog where she gives advice and design tips. Grant has bachelor's degrees in both business and interior design from the University of Central Florida and the International Academy of Design and Technology.