Did you try changing the clip placement on the carb needles. I am not sure where yours are set, but if you move them up one slot, that will lean them out just slightly, which should clean it up some. My 1999 ZR 440 Snopro is ultra sensitive to temp changes, and I do this on a regular basis. When it gets cold, I drop the clips a notch or two, and when it warms back up I have to move the clips back up. I run my '95 ZRT 800 at the second to the bottom slot for most riding, and 450 mains.
Good luck, and hope for snow.