b2000 dies shortly after starting

especially in the winter. It's been running rough in the summer too, though. Typically in the winter, when it's most pronounced, it will start just fine and then, after about 10 minutes of running, it will act like the carb is overloaded and almost die. Here's the thing, though: if I can get it to a place where I'm going downhill for quite a ways and can leave it in gear while I slow down, it seems to temporarily stop the problem.

Once I park it (for about 2 hours), go to class and then come out, it's fine for the rest of the day.