Lately, when mowing, it would back fire and quit running. After waiting for afew seconds, it would restart with no more problems. It seemed as though it was flooding. I changed the air filter, fuel filter, spark plug, oil and oil filter - after replacing these, it won't start at all. I switched plugs with no change. I pulled the flywheel and checked the pin, no problems. Can the coil be having an intermittent problem? Carb? Safety kill switches?