How fast does your stock moped run on flats with calm wind and moderate (10-20 C) air temperature?
My '88 moped does about 50-55 km/h(about 30-35mph).
It is a top tank moped with manual 2 gear (3 with neutral) transmission.
BTW does switching off the lights give me a bit extra speed (the generator makes as much resistance as much there is need for power). I have run it always with lights-that's the law...