MY LAWN MOWER STARTS UP WHEN COLD BUT ONCE IT HEATS UP IT STOPS AND WONT START UP UNTIL IT COOLS DOWN AND THEN IT DOES THE SAME THING AGAIN. I CHECKED THE OIL LEVEL, I CHECKED THE AIR VENTS, AND THE PLUG. I DONT KNOW WHAT ELSE TO CHECK. WHAT IS THE RIGHT SPARK PLUG TO USE IN CASE IM USING THE WRONG ONE.