I'm curious what would be considered the ideal exhaust diameter to run on a Lifan 125cc? I have one that I just swapped into a ct70 clone. I currently have a homemade exhaust on it made of 3/4" tubing and a briggs mower type muffler. I was attending a vintage bike night a few days ago and thought I would switch over to the original exhaust because it looks nicer. It is basically a CT70 copy, but I can see that the inner diameter is a little wider than the real CT70 exhaust I have on my '92. When I switched I went from a top speed of 54 mph down to 45 mph. Now I am looking to order an aftermarket exhaust setup, but I don't want to get something too small. I'm not trying to spend a fortune so I'm looking at some setups on ebay. I just don't want to put something on that's going to kill my top speed like the ct70 exhaust did. Is there a certain size tubing I should be looking for?