Thanks for the reply. I'm talking about a muffler/slip on. All I know is when I was a kid growing up in England in the early 80's, all the older kids had Yamaha RD125's and 250's, and they would put a Micron muffler, and/or the whole pipes, and instantly get another 10mph out of their bikes. If such an animal as a complete Micron pipe system exists for a 1974 CB550 I'd love to know about it?