Any ideas would be appreciated. I have a 2004 330 ATP, the kids were riding, said the engine would rev up, then lug down over and over again until it finally died. Now it will start but only with the choke out and only runs a second or 2, dies and back fires. It back fires just about every time. I have cleaned the carb and replaced the plug, it was firing good but I replaced it anyway. I'm getting fuel on the plug so I don't think it's a fuel problem. The valves were off and I thought that was the problem, reset them to factory specs with the help of a factory service manual, still no good. It does the exact same thing. What's next? sj