One of the most common non-injected engines available is that used in the R22 helicopter. Student pilots appear to roll them over regularly. I have seen these engines sold as not requiring a shock load inspection because the belt drive absorbs the shock. Two points here, firstly the idea that there is no shock is debateable and secondly if the drive drive train is disrupted under power where did the revs climb too? My guess is an overspeed. Be wary.