There are three screws associated with the carburetor. These are the Low Speed (L), High Speed (H) and Idle (LA) screws. The LA (idle) screw should be set for consistent idle without the chain moving. The L and H screws are used to set the mixture for low and high speed operation respectively. These are set at the factory and should not be moved except under extreme conditions such as use at high altitudes. The basic setting for these screws is to turn them clockwise till they seat. Then turn each screw out one and a quarter turn. If the idle is erratic or acceleration is poor, mixture is too lean. Rotate the L screw counterclockwise until the idle and acceleration are proper. If the engine exhaust smokes at idle, turn the L screw clockwise until the engine rpm decreases and then back one quarter turn. Make sure idle and acceleration are proper. After adjusting the L screw it might be necessary to readjust the LA screw for consistent idle. It is not recommended that you adjust the H screw without a tachometer such as the SenDEC STS-5000. The H screw is used to set the top speed. The top speed should not exceed 13,000 rpm. That should do it. Good Luck...
acerogers, December 2009
