It would be legal to run it on the factory engine, at which point the jet is just cargo. If you start the jet on a public road, it could be considered a public nuisance, reckless driving, etc.

If a the vehicle presents a clear and present danger of any kind it is a-priory a ticketable offence at least. With the jet off, it poses no such danger.

You can own a car, you can own a flamethrower, you can't fire your flamethrower out of your car while driving on public roads.

And for California, don't forget "Exhibition of speed" which is a rather nasty ticket to end up with.

I'm certain an officer could find all sorts of reasons to ticket that vehicle if inspired.

what I really want to know if he ever finished his scooter!