We had the same problem on a new Murray riding lawnmower (B&S engine) and we replaced just about everything we could think of i.e. fuel filter, etc. It turned out to be the carburetor fuel solenoid valve was sticking, so we replaced it. We believe the plunger was sticking causing it to malfunction, therefore the engine would cut out when the blades were engaged for a few minutes. The mechanic temporarily screwed a bolt in, until we received the new part. So far, so good. I'll update if this was not the problem.