Cold engine and colder temps Will do that. As long as its not excessively high idle, and after it warms up it when you blip the throttle it drop immediately back to Idle its fine. If it hangs at all when warmed up, richen the air screw a little at a time until it cures it. If it doesn't make any difference richen the needle by one clip position and reset air screw and repeat procedure until it stops hanging and is responsive when you feed it throttle.