My 2003 Arctic Cat 300 will start fine and will run. But it does have a problem missfiring about every 5 seconds. It is getting worse over time and when idleing it will die. I have checked the pick-up coil, flywheel, wiring and connectors, ignition coil, spark plug, and valve clearence. All are good. I'm thinking strongly that I have a bad CDI box. I know it is not the carb because a timming light shows the erratic missfiring. Is there any opinions out there? I need help.

 

My parents have 2 Arctic Cat 300's and they both do almost the exact same thing. Ive come to the conclusion that its the key switch thats messed up. If I turn the switch to where the headlights come on the thing runs like a top, but when I turn the lights back off it starts acting up again. Try turning your lights on and tell us how that does.

 

I tried that and it did the same thing with the lights on. Still believe it is the CDI. Thanks for the info--it sounded like a good possibility.

 

Check your voltage output. My AC 400 did the same thing. turned out to be the rectifier. It was putting out too much volts. If you are over15.5 (I think that is the magic number) you have a problem. I have an old post on here about that which has all of the specifics.