I was a friend of the late, great, Herb Ottaway. He was the inventor. If yours says Jacobson, someone put that decal on after it left Chance Ind. All production models were labeled Hop Rod. The first prototype had a lawnmower engine and a throttle. The idea was you could lean forward and make real time with a throttle. Instead, it just became a jackhammer, and would hardly move at all. I recall 5 prototypes, and two production models. All still exist. The first production model had exhaust ports facing forward and backwards, oiling and heating your socks, shoes, pants, and legs all at the same time. The rear exhaust port was left undrilled in the second model. How high you could hop depended on your weight and body english/jumping power. An agile, light, kid could get 3-4 feet off the ground with a lot of effort and technique. Part of that height was pulling the Hop Rod up higher in the air by bending your knees and pulling it up at the peak of the jump. If standing fairly straight, the max height is maybe 2 feet. It really doesn't look like much when watching an adult ride one. Except for the time I saw Herb riding one, waving his cowboy hat around his head, and hollering "Yippee!" as he demonstrated it for a crowd. I have three of them, and both production models, original box, store poster, and a couple of cans of Po-Go Go, the fuel. They are kinda cranky to make run right, and it is true there were a few injuries out there in consumer land. Danged lawyers ruin all the fun!