I've run several of the 2 strokes, different suppliers, 49cc and the larger one. All will run for hours at moderate load, 20-30mph on flat surfaces. Use good oil, at least 32:1. They don't like rpm or hills, so help out with the pedals on the up-hills and disengage on the down hills. Keep your gears greased.
I've overheated and over revved a couple times, but I was trying to run it to the max. One head cracked while hill-climbing and hot.