I love this stuff.
I adapted a small 2 cycle lawnmower engine to my Sting-Ray style bike when I was in junior high, 1967.

The engine had a belt centrifugal clutch feeding a 10" belt pully at the bottom bracket, across to a small sprocket made from a rear cog, feeding a chain to the rear wheel which mounted a large sprocket made from a front chain-wheel. All of the parts were welded by my older brother who was in high-school metal shop.
It was scary as hell to ride, in the grass field across the street. My stupid friend was stopped by the local cop doing 35 on the street.