I have a 1996 Polaris XCR 600. It was starting in one or two pulls when I first got it and it stayed running fairly easily. I haven't done anything to it, and now it starts hard and when it does start, it doesn't want to run for longer than about 10 seconds or so. A friend and I pulled off the carburetors and they were totally clean, the jets are at 160, stock size. The only things I can think of to explain this is that my friend said the carbs look like they were overbored, they look like they have been machined out. And the other thing is when I got it, it was about 40 degrees out, and now it's more like around 20 to 10 degrees. Does anyone know what this could be?