That looks good. What about the opening? How big must the exit hold be? I cut one down but made the exit hole to small. I was only getting about 6000 rpms out of the engine. I pick up and b&b and just used that on a 25cc engine. I have some aluminum square tubing that I was going to try to make some out of. and I was going to try alumoweld and see how that will work. but not sure on how hot the muffler gets.
Paul