The low speed needle is the screw in the center of the throttle arm on the side of the carburator opposite from the high speed needle.

Start with the high speed needle 2 1/2 turns out. Go to full throttle and turn the high speed needle in slowly until the engine runs smoothly. Then turn it back out until the engine just starts to slow down. Shut the engine off. Now screw the low speed needle in 1/4 turn and start the engine. Shut the engine off and turn the low speed needle in another 1/4 turn and restart the engine. Do this 1/4 turn at a time until the engine will no longer start, then turn it out 1/4 turn and you should be OK.

Make sure you have fresh fuel and a new glow plug before you do this. Also watch for bubbles in the fuel line. If you see bubbles, you have a fuel feed problem and you can not tune the engine until you eliminate them.

Jim