When I was a kid in the late 60's my brother had a mini bike, Fox IIRC, that we mounted a Mac9 go kart motor to. We had a family friend that raced Karts at the time and he gave it to my Brother in exchange for some yard work. It was dual carb'd and made about 21HP on alcohol. .It would run on premium gas if you stuck a sock in one of the intakes and make about 15hp that way. It was direct drive and stupid dangerous to ride.We had it to a seat of the pants 90mph which was ALSO way stupid considering the wheel size/wheel base and lack of proper brakes. Even starting the thing was a dangerous thing as it had no clutch and only a paddle rear brake to stop. It DID have a kill device that would ground the spark plug and stop the motor. Things you do when your young and dumb!!!