Originally Posted by Creative Engineering
I checked the tooth count on the primary gearset, 20 crankshaft, 82 clutch.
At 21 MPH with a 36T rear and 10T front your engine should be turning 4,008RPM.
This should be well eough into the power band for it to keep climbing.
We actually had a similar problem on ours, but it had nothing to do with a sprocket ratio change.
We used non-synthetic oil and the factory plug during break-in. Right at the end of the break-in the engine would blubber at upper RPM's.
We changed to a high grade of synthetic, and an NGK B6S plug. It made a HUGE difference.
You might have hit the nail on the head. I ran some other gas that a friend had about the time I changed sprockets. I'll get another new plug and try it with fresh gas