OP

I dont think you have gone so far as to gum up the carbs. For the helll of it I would just add a little seafoam to the tank. The main problem is that I dont think you are warming your bike up long enough. The new 250s are super lean down low to begin with so that helps explain a little bit of the stuttering and the cold weather and it sounds like your problem. I say let it warm up a bit longer and report back.