I don't have the bikes you're listing but I do have a Honda horizontal engine 125cc clone bike. It has a fully automatic transmission. It easily will do 45mph but gets loud and buzzy as you say. I think if it had a standard transmission with the right gearing it would go faster and be much smoother. I believe I am running the PZ19 carb with cone filter and I drilled out the exhaust to open it up some. Drilling out the exhaust made the biggest improvement in power/speed.
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