MY CRAFTSMAN 2 36 INCH 12HP BRIGGS & STRATTON RIDING LAWNMOWER CRANKS OVER BUT WILL NOT START. IT WAS RUNNING FINE BUT AFTER RUNNING IT OUT OF GAS AND REFILLING, WOULD NOT RESTART. I HAVE GOOD SPARK AND FRESH GAS BUT IT WILL NOT FIRE UP. I HAVE CLEANED OUT THE CARB AND SPARK PLUG.THE FUEL FILTER IS GOOD AS WELL. WITH THE AIR FILTER REMOVED, FLAMES WILL COME UP OUT OF THE CARB DURING CRANKING. PLEASE HELP.