I have a 2001 300 king quad that runs fine prowling around in the woods at lower speeds less than 15 mph. Lately it has started wanting to stall out after high speed operation of high RPMs such as climbing a steep grade. If it sits for just a few seconds, it wil start and I can rev it up and then it will idle fine. I have had it in twice for this and was told it was a dirty carb, so I have now put a filter in line between the carb and tank. I dropped my gas cap and the peices separated, so I screwed the valve back onto the cap and it seems that I can blow through it OK. Could it be the gas cap? It has 1300 miles on it, so I was wondering if the valves could be causing this issue.

Thanks