- 1). Place the engine on a hard flat service.
- 2). Remove the air filter cover from the top of the carburetor. Slide out the air filter and inspect it. If it is dirty, replace it. Re-install the air filter cover. Place your engine in a position where the spark plug is facing up. On the right side of the engine, pointing up from the carburetor, are three small screws. These are your speed or timing screws. On the carburetor under the screws are their markings: "H" for high speed adjustment, "L" for low speed adjustment, and "I" for idle adjustment.
- 3). Start the engine. Turn the "L" screw clockwise until the screw seats, and then back out one full turn. Then adjust the screw in 1/8 turn increments until the engine runs smoothly in the idle position.
- 4). Turn the "H" screw in until it seats, and then back the screw out one full turn. Rev the engine to full throttle, Keep turning the screw in 1/8 turns until the engine runs smoothly in the full throttle position.
- 5). Slowly turn the "I" screw clockwise while the engine is idling. If you're adjusting a string trimmer, keep turning till the trimmer head starts to turn, then slowly turn the screw counterclockwise until the trimmer head stops. If it's a chainsaw, slowly turn the "I" screw clockwise until the chain on the bar starts to move. Then slowly turn it counterclockwise until the chain stops. Accelerate the engine several times to ensure proper adjustment.
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