I loan my C-120 with the Kohler Magnum 12 to my dad he put old gas in it. I rebuilt the carb , drain the gas tank and change the spark plug. Problem is it stall out under a load after a few minutes. I checked the spark after it stalls to see if it was the coil was breaking down but it still has spark and the gas vent is clear. It Idles forever but put under a load it dies after awhile. Any ideas ???