assuming its a 66cc China girl- you're in for a struggle getting that kind of speed-
maybe a souped up version, with a jackshaft and shift-kit can get up near that-
the limiting factors are the one gear and the motor power itself-
If I wanted top performance right now without a lot of special mods- I'd take a 66 motor and get the wide intake spaced jug and put that on- with a billet intake for a wider intake CNS type performance carb- surest way to get more fuel to the motor- wider intake on carb and wider intake on the jug-
see my 66 bike here- THIN 27 x 1/1/4 wheels with alloy rims for fast rolling, and great pedaling-
and with a 34 alloy sprocket-
the smaller the rear sprock the faster the top end, but you may have a harder time pedal starting or peddling assist until it can kick in-
this bike will cruise at 30, but only top out about 35- with no special mods to the motor other than a billet intake and kit Speed carb.
Havent used high compression head, but that would probably help, as well as some kind of expansion chamber exhaust-
not interested in that- the bike makes too much noise already- that longer pipe is never coming! Got as much speed and power as I'd ever be comfortable with- and that's after racing USCF road for 14 years as a young foolish thing.