I have the same problem with the a similar engine (18.5 H OHV, B/S 31P777-0293E2). Starts fine, runs well for about two minutes, then gas floods into the air intake side of the carb from the crankcase breather tube; the engine sputters and dies. Can't tell which happens first, flooding or choking (almost simultaneous). White smoke everywhere (neighbors, wife, annoyed). Engine re-starts reluctantly, then the problem repeats, only sooner. Removed and cleaned the carb - everything looked fine. Need advice.