Reading the post here reminds me of the time when I was very young my grandfather built a motorbike for my uncle. This thing had a Briggs & Straton engine with a rope pull starter. I remember all this well for I destroyed the bike. The drive was belt to the rear with a idler down by the right foot. Gave it gas with a thumb lever off a lawn mower and the idler built in the shape of a "V",you stepped down on the front of it and the idler went up in the back making tension on the belt and it took off. Want to stop release the idler. Really worked excellent until a seven year old hit a hole and the front wheel came off. The trip through the air was fun the stop not. That same design could be used today. 