5 Steps to Fix Surging on a Stihl MS 261

Start with the air filter A dirty air filter causes surging. Clean or replace it before adjusting anything.

Check for air leaks Inspect fuel lines, the carburetor boot, and the tank vent. Cracks or loose connections let in extra air and cause surging.

Turn the low-speed screw counterclockwise Surging usually means the low-speed mixture is too lean. Turn the L screw out in 1/8-turn increments.

Let the engine idle between adjustments After each tweak, let the saw idle for 30 seconds. This lets the carburetor stabilize so you can judge the change.

Leave the high-speed screw alone Only adjust the H screw when tuning under load with a tachometer. Guessing will damage the engine.