Mid-sixties I had a Kawasaki 50cc JTRL, which I can't find on the net, but it was like a regular motorcycle, but smaller. I bought it just in time since my car crapped out and I had to drive wife to work on it until the car was fixed.
Had an oil injection system so you didn't have to mix fuel and a large sprocket for trail use. Oil injection was adjustable, but nevertheless, the thing fouled plugs all the time. There was even a compartment in it for a spare plug and, I believe, a plug wrench.
Changing the sprocket for street / trail use was a bit of a pain. There was a length of chain with quick-detach links for the larger sprocket.
Nevertheless, it was a lot of fun and even after I got the car fixed, I put a lot of miles on it tooling around the Boulder Colorado environs.
Terry