My suggestion would have to be a larger carb. Once the intake and exhaust ports are cleaned up, the engine breathes soooo much better. I am running a 18mm carb along with a 48cc tuned pipe and have a much wider powerband, and better top end. With the stock carb the powerband would end because the engine couldnt flow anymore than the 14mm carb would allow, and it much smoother going from idle, to mid, to wot, if jetted, and set up correctly. I believe a pipe without a larger carb is not worth it.