You gave him the motorcycle while retaining title in your name? Do we need to tell you how foolish that is? What if he causes an accident?
You don't get to take back the motorcycle and keep the car merely because he owes you some portion of what he agreed to pay for the motorcycle. If you do that, you can expect him to sue you for the return of money. You didn't share the full dollar figures, so we're not in a position to comment on how much that might be.
If you want to make a claim for the remaining balance he owes you, small claims court awaits.

