I have a 6.75 hp Eager 1 Craftsman ( model # 917.377582 - green walk behind, self propelled, rear bagger). Mower always ran good for me. This year I started it up this year and it ran poorly. I took the lower carb (bowl) off cleaned it out, blew it out with air ran a wire bristle thru the little venturi holes replaced the primer gasket on the carb. Now I started it up and runs good for about 15 mins then it starts to puff out the exhaust, not smoke or anything just extra puffs of exhaust. Then it runs rough, stalls out and I have to wait for it to cool down. Then it runs good and starts the process all over again. Any Ideas? no gas leaking anywhere.