Cold Weather Making Bike Lurch

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I have a 2003 GZ 250 and had noticed the bike was lurching slightly when running in the top ends of first and second gear. Knowing from other issues with the bike in the past that the previous owner was a sack of potatoes who cared nothing about routine maintenance, I took the bike in to have the carbs looked at. Sure enough, when I got the bike back they cleaned the carbs out, put in a new spark plug and new air filter. The bike ran better than ever.

Now that the weather is getting colder here in Iowa, the bike is having all the same issues as before, temperature dependent of course. Colder the weather=worse the issue. I've been riding it in 30-40 degree weather and it is hating every minute of it. But on a little warmer day (50-60) it works out of it pretty quickly and the issue is almost not noticeable. Is this a mechanical problem, or is the bike just prissy?

Thanks