Nice spec, what sprocket setup are you running and what top end do you get?
I'm running a 110cc semi loncin lump, just stock carb. Don't really feel the need for more power.
Sprockets 17-37. Hits a max of 50mph on straights, Don't want to gear it more than that because I rag it about offroad. And lets face it, with these bikes that requires skill.
Drums I find are perfect for my build. As you say, discs are probably better for your bike. Depending on the top end?? (any slower than 55, id say drum, any above disc maybe the better option)
Not sure how the stock jincheng lump manages 40, my stock 50 lump only managed to pull away in first with me on it.
Hence the 110.
Although to be fair, can't see why you'd want to go more than 55mph in the first place. Too many speed cameras.