Hello!
I have a 1996 Polaris Sportsman 500 that I rebuilt and now after a couple test drives, it ran excellent and was just about ready to put the plastic back on, but it suddenly developed a terrible mis-firing issue. It will start, but will only fire about every half-second. Immediately dies if you bring it down to idle. It can be throttled up, but it will never run smooth. I took it in to let the experts figure it out. They put in a new plug and noticed that the air filter was flooded with fuel. They checked the cam timing and said it was good. When I got it back from them it actually ran OK long enough to drive it from the trailer into the garage. The next day it was back to its old ways. I noted that it had leaked a great deal more gasoline into the engine oil. When I went to put a new carb in it, the oil cooler was full to the top with fuel. I drained that, put in oil and put the new carb in it, thinking that the float wasn't closing. I'm not seeing fuel leaking into the engine oil any longer, but it still fires only sporadically. The spark coil and CDI box were not very expensive, so I figured they would be a good gamble. I lost that bet. Still runs like crap.

What now? The magneto/exciter coil?