High Speed Needle Valve
The high speed needle valve is used to meter the air/fuel mixture at full throttle. Turn the needle clockwise to lean the mixture or turn the needle counterclockwise to richen the mixture. When you start the engine for the very first time the needle valve should be turned in completely, then backed out 2-1/2 turns. When you start the engine after that, leave the needle valve in the same position it was in when you shut down the engine.

Low Speed Needle Valve
The low speed needle valve regulates the air/fuel mixture at idle and during transition from idle to full throttle. Turn the idle mixture screw clockwise to lean the mixture. Turn it counterclockwise to richen the mixture. The idle mixture screw is preset from the factory, but minor adjustments may need to be made. To reset the mixture screw to the factory setting open the carburetor barrel completely. While holding the barrel open, turn the mixture screw in until it stops. From this point, turn the mixture screw out 2-1/2 turns. This is the factory setting.