In 2009 the Harley Davidson changed the body of the 50mm fbw so it can not be enlarged. You can make the throttle plate bigger but the body of the throttle body is too small to notice any benefit from a larger plate. The after market industry has risen to the challenge of making these better. HPI and S&S have made their own larger casting of the throtle body from 51 mm all the way up to 70mm depending on motor size. What needs to happen if you want a larger throttle body is to send me your origninal throttle body. I will prep it for shipment to either of these companies. What happens when the throttle body arrives at these companies is they are going to remove all the internal electronics out of the throttle body and install them into a new casting of the size you want. This the only option on late model, (2009 to present) throttle bodies.