I saw a clip of those on TV. Not sure how they soup them up, but they change the drive gears around so instead of a lot of power, they have a lot of SPEED.
The idea is to drag race with them maybe 50 yards. All were walk behind, so they start at the line, rap them up and launch. Most I saw were being DRAGGED within a few yards as they couldn't run fast enough to keep up with them.
Amazing what the bored adult male can come up with, right?
That's a motorcycle Engine that he's got on the tiller. It looks like a triumph or maybe a Yamaha twin from the early 80's.
Guys will do all kinds of stuff with these old engines. Here's one where someone converted his Allis Chalmers tractor to a Yamaha XS 650 motorcycle engine.