I had that happen to me once on a 5 Hp briggs horizontal shaft in the tech room, my teacher told me it was blowing by the rings or the timing was off, the motor only ran for about 30 seconds b4 it died again. I know that is a small engine but all 4 strokes have the same concept and run the same way. Up, open a couple valves go back down. Streets can forbetter my response and confirm one of the circumstances I have given you or give a correct one if any of mine are not correct.