As braahp mentioned, to compensate for the greater O2 content of colder air you'll need to richen the mixture. The pilot circuit can be adjusted with the air screw (assuming that it isn't turned beyond 3/4 in right now). Depending on how cold it gets by you and how long into the winter you ride, you will want to go with a richer main jet, one to two sizes. You will likely need to drop the clip on the needle too.