it put this system from nrc into my 93ccm engine at the cy80. carebutor pc10b, exhaust from xl75, cdi standart.
maximum speed is ~9okm/h
i don´t have any experiences with that performance at a 50ccm engine.
andre tried it at a cy50 with 62ccm zeta-set. his max speed is about ~60km/h.
it´s not very difficult to install the nrc system in your engine. it´s nearly "plug and play" but you should know something about electrical circuit of your cb-cy-xl50.
there is a difference between the flywheels 140, 130 and G4: the rabbet of the G4 flywheel is 4mm and on the crankshaft is normaly 3mm with the original flywheel