I've never had one, but I've heard stories about engines that can be taken apart and the direction of rotation reversed. You'll know if yours is one of these if you can take the back-plate of the engine casing, and swap it with the assembly containing the carb, shaft etc.. If the casing is one piece from thrust washer to backplate (like most) then you obviously can't reverse it.

FYI, I have a K&B .25 that ran once in 1980, and sat in my garage until 2001. It ran pretty well for a season, but finally gave up the ghost a few months back.