I have a 1986 ATC200X. The person who had it before me put a 1984 carb on it (PD62). What is the difference between a Keihin PD62 and a PD64? Is there performance to be gained back here by switching back to the PD64? Also, what other alternative carbs could be put on my '86 200X to increase performance. Perhaps a PWK?? I am in the process of rebuilding the engine. Mild cam will be used in conjunction with decking the top of the cylinder by 1mm.