what exactly does this control? I have mine set on 3 turns out like HMF said, but my friend who has an HMF full system like me, with a hot cam stage 2 and a higher compression piston (not sure on the exact compression) has his 2 turns out. They both seem to run ok, other than mine shoots flames occasionally. Could the cam and the piston mean the difference in this?

 

The cam will make a difference in jetting. Blowing a flame is normally from too rich of jetting. The air screw controls just off idle to quarter throttle. Try turning the screw in a little at a time and see if it starts to run better.

 

Maybe your friend is running a bigger pilot jet and/or moved the needle clip in a lower slot. Either of which would require less turns out on the air/fuel screw.