When I raced dirtbikes, a local guy used to fix dented twostroke pipes, because dents can render the power of a twostroke. He used to plug one end of the pipe with a cork and the other with a hole just big enough for a air nozzle to be inserted well anyways you heat up the area with a torch and then shoot burts of air into the pipe pushing the dents back out. But it can be dangerous and the heat would probaly ruin the finish on your pipe. but if you dont care about the finish then try it. It always worked for us.