I don't know I've never put a tach on one to find out I just rev it until it won't go no faster, but only under a load don't wind it out with out a load or the insides will very quickly be on the out side.
Wild,Are you saying 50MPH! What sort of setup you running.With my 44 tooth 70cc anything over 27MPH is like those old test pilots trying to break thru the sound barrier.Handlebar vibrates to the point where it's almost painful to keep your grip.Ron