So I just put together my third build. On my way home from work the exhaust cap rattled off and I have to say this bike rips now. At first I was concerned and ordered an expansion chamber to see if I could keep the increased HP with a more free flowing exhaust. The expansion chamber didn't exactly give me much more HP than a stock exhaust, took forever to warm up in 40 degree weather, sputtered uphill, caused excessive vibration, and eventually vibrated right off. So I am back to the exhaust with no cap. Without a cap I have more HP, it zips up hills, and it warms up quickly. Also, I like the fact that it's a little louder. There is no substitute for expert riding but there is also something to be said about loud pipes. I ran Harleys with drap pipes for years and I think I am going to keep this 49cc eggbeater unmuffled. It runs better and makes me more noticeable.