For one, a single credit card usually doesn't build a lot of credit in the lender's eyes.
However, that money down makes a difference, the loan is easier to get with that kind of $$ as a downpayment.
I used to sell cars/get customer financing, and if you put 40-50% down on a car, you're getting a loan in most circumstances. Only thing I'm not sure of, is bike loans are harder to get than auto loans, so that may effect your chances.
My suggestion is to go online, check capitalone and Eloan, then apply online to see if you can get your financing secured BEFORE going to the dealerships. A couple reasons why: 1) you know what you're looking at in terms of how much bike you can buy, and what rate you're approved at. 2) If you go around to different dealers asking about financing, they may "shotgun" your application to numerous lenders, putting a bunch of inquiries on your credit, which can lower your score.