These dry clutches work just as On and Off. motorcycles and cars use clutches that are variable, opening it slightly permits slight power to the wheels. I don't know the exact workings of automobile and motorcycle clutches, but they are pretty complicated.
I think a better clutch could be disigned for these motors only the power was converted through a jackshaft into a belt drive, and mount the clutch somewhere on that. use the original only for starting the motor. I can't put what I'm thinking into words correctly.