Utterly Fazed

Sounds like needle valve or float height. Do you have one plug running black? or at least darker than the other, chances are that is the problem cylinder/carb.

My Son has one of these bikes and he struggles to do more than 63mph, (when the speedo is working that is ) there has to be a way. My thoughts: Has anyone tried blocking off the small take off pipe from the exhaust that goes to the emmissions stuff? The outlet on the std exhaust seems very small diameter, does a replacement exhaust help much? Can anyone confirm this restrictor in the front of the exhaust?