Two of my friends in High School had Whizzer motorbikes..I guess they were WWII or post WWII vintage. A huge ring-shaped pulley mounted on the rear spokes made of stamped sheet metal, and a 1 cylinder 4-Stroke of about 5 HP.
There were also VeloSolexes, with a microscopic 2-Stroke mounted on the front fork with a rubber drivewheel that ran against the front tire.
They were fun. The Whizzer had a compression release, so you could pedal the heavy Schwinn and get it rolling then slam the valve shut to get it started.
Maybe they will come back. There is a hub-mounted electric motorized front wheel that can be dropped into contemporary bikes now.
The Whizzers HAVE come back.
You can buy replica kits pretty cheaply, and there is even a company here in my little town, with a long waiting list, that builds HIGH quality, high buck custom replicas.
I’d go electric though if doing it for practical use.