If he is the registered owner of the motorcycle, you have a problem. You would have to sue him for ownership of the motorcycle and have a basis for the claim. As of right now, it seems that you have a claim for money damages - you loaned him the money and he is responsible for the payments. As there are recurring payments, you may want to sue for the entire amount of a payoff for the loan. A bigger problem is that (a) the bike may be repossessed and you'll be liable to pay the repossession fees and costs, and (b) your credit will take a major hit. You may wish to tell him that if he doesn't give you the bike back, it may be repossessed and you will sue him for the additional costs as well. The free ride will come to an end soon.
