I've had the lawnmower since 2002. This year (2013) after mowing for 20 to 30 minutes the engine will start to die. It gets down to a idle and then starts up to full throttle again. It does this several times and then finally will die. If I let it cool for about 1/2 hour and start it again, the routine will repeat. It seems to be heat related.
Doesn't sound heat related to me. More likely a lack of fuel. First thing to try is easy, next time it starts acting up, loosen the gas cap. If the engine returns to proper running, your cap has a clogged vent and I recommend replacing it. If that does not fix it, I recommend removing the carb, give it a good cleaning and when you reassemble, make sure that your install a new float needle and seat.
