Three adjustments are provided in the carburetor. They are the main adjustment needle, the idle speed adjustment screw, and the idle fuel adjustment needle. There are three factors that control the conversion of the fuel / air mixture into engine power. These factors are engine compression, ignition, and correct carburetor adjustment. Correct carburetor adjustment cannot be obtained unless engine compression and ignition meet specifications.
Before proceeding with the carburetor adjustment, the following preliminary steps should be performed to be sure the adjustments are made correctly:
1. Set the idle speed adjustment screw so that the throttle plate is slightly open.
2. Make certain that the fuel tank shut-off valve is in the open position.
3. Pull the choke knob, turn on the ignition, start the engine, and push the choke knob in until the engine runs smoothly.
4. After the engine has reached normal operating temperature, be sure the choke knob is pushed all the way in, and proceed as follows:
For the initial setting, before the engine is started, turn the idle fuel adjustment needle in (clockwise) until it is seated lightly, and then back it off approximately one turn. Start the engine and turn the idle fuel adjustment in (clockwise) until the engine begins to "roll," then back it off slowly until the engine is running smoothly.
With the hand throttle in the closed position, turn the idle speed adjustment screw until the engine idle speed is 450 to 475 rpm on the Proof-Meter. On new engines, it may be necessary to set the idle speed slightly higher to prevent stalling.
The power fuel adjustment or main adjustment needle initial setting is 1 to 1-1/4 turns open (counterclockwise).
The final adjustment should be made in the field. With the engine running at governed speed under full load, turn the adjustment needle in (clockwise) until the power picks up and the engine runs smoothly.
