does it sputter out and die? or just die like you flipped the kill switch?
another tip. have a can of carb and choke cleaner handy, and keep the air box open. start it, and when it starts to die give it a small dribble of the carb cleaner. if it revves back up, you have a fuel supply issue, not enough fuel is making it out if the carb, into the engine. if it kills it, you either sprayed too much, or youre getting too much fuel into the cylinder.
Does your carb have 3 adjustment screws? if not, I'd recommend getting one.