Just what Josh said. The boat has a metal tag on it indicating the max. hp. If you have a higher h.p. than whats on the tag, you could be fined.
In being a jon boat it has a flat bottom opposed to a v hull so I bet it wouldn't be more than about 10hp. In being a flat bottom, it doesn't handle wakes/waves very well as a v bottom cutting into wakes/waves.

Bobby