Hi Dave the mixture screw is for pilot or slow running only, and its usual setting is 1 1/4 turns out from (gently) being turned fully in. The only other mixture adjustment is the needle in the throttle slide.....there are usually 3 or 5 grooves for the needle clip to locate in, and its held there courtesy of the throttle return spring. Keep the needle in the middle notch. The needle governs fuel mixture from 1/4 to 3/4 throttle - after that fuel is governed by the main jet size. I really can't comment about the variator balls function - its something I know nothing about - sorry! It may be worth having a natter with someone at a local scooter shop - hopefully they'll have seen this before.
As you don't seem to be getting anywhere really - maybe the fault is not in the carburation side after all? Best of luck! John
John
October 2009