I have just had my motor rebuilt (2000 model Wolverine)with a 11:1 Piston, Cam, HD Valve Springs, ported and polished head, Mikuni Carb with built in fuel pump running on race fuel 50/50 with pump gas.

The problem is from one third throttle to two third throttle. There is minor bogging and sputtering/coughing as it gets up into the higher RPM's. Once it gets above two third throttle it takes off like a two stroke and pulls hard all the way up through the gears as long as you stay above two-third RPM's.

Thanks for any help or suggestions you have.

try raising your needle a clip at a time.it seems as if you're running lean in the mid,and that would be your needle.