I have a 1994 48hp spl that starts and idles fine. As soon as it runs for 10 minutes or so it starts to chugg and loses power, both on muffs and in the water. If I throttle back it will idle fine. Carbs were just done, as wellas a tune up with new plugs...ect. New gas line. bulb stays firm. Don't know why this is doing this.