Sorry, I misspoke when I said I didn't need help with the design. I meant I know the general setup I want, and I plan to make this fan-powered- and thus more unique. I also should elaborate a bit more: I plan to use a standard 4-stroke 1.5 horse engine, it has it's own cooling fan, as the power plant, and set it up with a pulley system & jack shaft to get more rpms out of the prop.

This whole idea is based on this: www.instructables.com/id/Propeller_Powered_Skateboard_1/

How do you determine the size and pitch of the fan ( I had thought that a 24x12 might work) and horse power of the engine?

If the fan were to be mounted off the back of the frame, how much space should there be between the mini-bike and fan so that the fan isn't starved of air?