I have a 04 LTZ 400 I just picked up. It's completely stock as far as I know besides an upgraded k&n style air filter. I recently flushed all the fluids and cleaned the carb out as well as replacing the main jet o ring that was corroded and replaced the spark plug. The issue I'm having is that the bike starts right up and idles perfect and revs fine at any rpm when u hit the throttle but as soon as it's warm, if you hit the throttle quickly it will bog and sometimes die. If you gradually increase the throttle at a smooth rate it revs fine. What could be the issue?