Assuming the sales contract is valid and you made all of the payments required under the contract, your friend breached the contract by refusing to turn over the motorcycle.
A good first step would be to send your friend a demand letter (send it via “certified mail with return receipt requested” so you have proof that it was received). The demand letter should include a copy of the contract and receipt, and should threaten legal action if the motorcycle is not turned over in a certain number of days.
If the motorcycle is not turned over, you’ll need to file a breach of contract lawsuit in court. If the motorcycle is worth $10,000 or less, you can file the lawsuit in small claims court without an attorney. If the motorcycle is worth more than $10,000, I would consider hiring an attorney to file a lawsuit and represent you in circuit court. You can find an attorney near you using our free online directory.