Diagram11
1. High Speed Needle Valve

 

2. Low Speed Needle Valve

3. Choke Lever

 

4. Idle Speed Screw

 

Turn both needle valves clockwise until they seat using caution not to over-tighten as it may damage the needle valve or seat. Turn the high speed needle valve (valve towards the front) counterclockwise 1-1/2 turns. Turn the low speed needle valve (valves towards the rear) counterclockwise 3 to 4 turns. Both these settings are good starting points. Start the engine and thoroughly warm up making sure the choke lever is fully open before starting on any following fine adjustments. With the engine at an idle (throttle closed position), fully retard the spark and adjust the low speed by turning it either clockwise or counterclockwise until the engine smoothes out and fires evenly. Turning this valve clockwise gives the engine a leaner mixture while turning it counterclockwise gives it a richer mixture. Rev the engine up to about throttle and hold steady at this rpm to adjust the high speed needle valve. Turn the high speed needle valve clockwise until the engine starts to falter. At this point turn needle valve counterclockwise until the engine runs at its fastest speed. Check this adjustment by retarding the spark and opening the throttle. If the engine backfires through the carburetor it indicates a too lean a mixture and the needle valve should be turned counterclockwise a little. If the engine chokes when the throttle is opened, it indicates a too rich a mixture and the high needle valve should be turned clockwise. When making each adjustment, slowly turn needle valve a notch or 2 at a time giving the engine time to respond. Once settings have been finalized note the needle valve location so as you can return to it if anything should happen. Although the high and low speed needle valves operate independently, they do affect each other. For this reason, return to the low speed needle valve and readjust as in step 4. Adjust idle speed by adjusting the screw on the throttle shaft bell crank. Turning it clockwise increases the engine speed while turning it counterclockwise decreases engine speed.