If the radio problem showed up, at the same time the loss of power did...I would check the charging circuit, to see if something is loading it down heavily. This is only an educated guess, since I don't even know what brand of bike you have, or have the wiring diagram for it. An alternator with a bad diode in it, or a nearly dead short on its output, can act as a brake. If your bike uses other electrical accessories, or electric start...and the battery is being charged properly, and the other accessories work ok...then I would start looking for something binding or dragging, in the drive belt system. Especially, if the last belt wore out quickly. Good luck.