Are you referring to the red on/off valve that is on the line running to the carburetors?? If so, that is the heated carb line. If on, it will circulate hot coolant from the engine through the carbs and heat them so you don't have the freezing carb syndrome. A lot of people, me included, delete that system. The manual says to use it when you get below zero, but I have never had a problem or needed to use them, therefore I deleted it. I'm sure someone else will chime in with why you DO need them....what is the red on/off valve for I just noticed that this week? and should it be on or off?