All the motorbbikes I have built have been based on bike frames and the footrests are WAY high compared to cycles. I think I still have a Moto Beta frame upstairs It might be a good mount for my 100cc Guazzoni GoKart engine. It is 8-1/2 HP and supposed to turn 15,000. It has a centrifugal clutch. I could rig a sliding center double pulley with a rocking foot peddle to change the ratio. The Cerianni fork that was on it is now on my 6-1/2 HP bike with a 3-speed Sturmey Archer hub tranny for a jackshaft. I need it on that one because it has a huge disk brake and at about 55 tops it NEEDS it. I would hate to cannibalize it. Maybe I can put a 30's Indian type leaf spring fork on it and find another skinny (2.75) front wheel with a disk.