I just boughtg a Tecumseh Power Sport Horizontal Engine - 5.5 HP, 3/4in. x 2 3/8in. Shaft, Model# OH195EA-71241G as a go cart replacement engine. Bolted up and all just fine. Cranks and idles well. When you drive the go kart for 7-10 minutes, it fouls the plug and dies. New plug, repeats process. Choke is NOT on. Engine lugs a bit and smokes on acceleation. CArb is new type with no mixture adjustment. Metal plug on side of carb may cover mixture screw??. The engine is 3 days old. I'm on my 4th plug, a hotter plug didnt help. Engine runs rich. Any idea how to lean it out? I know I could return the engine, but its mounted and all set up now.