You indicate that the sale occurred in New Jersey, so if you want to sue you need to sue in New Jersey.

There are no good answers here -- you should have insisted upon being paid in full when you 'sold' the motorcycle and transferred title to the buyer. Now you're not only out the money and the motorcycle, you are potentially civilly liable if the 'buyer' causes an accident and can find yourself being billed for his parking and toll road violations.

Options include trying to get your 'friend' to return the motorcycle, trying to find a way to collect the motorcycle (since it is still in your name), offering him a discount if he pays by a specified date, transferring title to him and writing it off as a life lesson, suing in small claims court....