If you have bad credit you have two options. First, you could get a secured loan from a bank by using your personal property as collateral. If you own a house or car you can use it so that they will give you the money you need for your motorcycle. The second option is having a credit worthy friend/relative that has good credit to co-sign on the loan with you. This means you friend/relative will be promising to repay the loan in the event that you are unable to pay it back.
Sort your credit out- don't get yourself in deeper trouble.
Buy a cheap, old bike- still fun.