Sounds fuel related. It might be as simple as the changing fuel mixtures they sell to account for temp.
First step is to adjust your hot idle to 650 or so. If that doesn't solve the problem, then you may have to look a little deeper.
Also pull your plugs and see what color they are at the tips. You should see a uniform light/tan color. The threads can be oily, but if the tips are black/brown....you either have a misfire, or your carb is running very rich. Both will cause the symptoms you're having.