A Ryobi carburetor needs idle adjustments from time to time. However, any other adjustments should be made by an authorized dealer. The only adjustment that usually is necessary is to make sure the engine stays running while idling and that the trimmer head does not rotate. It might take several attempts before you can adjust the idle speed. If you still have problems keeping the engine running after making adjustments, clean or replace the air filter.
Locate the idle-adjustment screw on the Ryobi trimmer. On the four-cycle Ryobi, the idle adjustment screw is directly below the primer bulb. On the two-cycle Ryobi, the adjustment screw is through the air-filter cover. You do not need to remove the cover to access the adjustment screw.
Start the Ryobi engine, and hold the trigger to allow the engine to stay at a high throttle speed for one minute.
Release the trigger, and allow the engine to idle. If the engine stalls out, turn the adjustment screw clockwise one-eighth of a turn with a Phillips-head screwdriver.
Start the engine again, and test the idle. Continue making adjustments clockwise until the engine stays running without stalling or coughing.
Examine the trimmer head while the engine is idling. If the head is turning, adjust the idle screw counterclockwise until the trimmer head stops rotating while the engine keeps running.