Snowmobile Repair: Backfire, arctic cat zl, champion powersport

Question
I have a '99 Arctic Cat Zl 440, when i rev it up and get to about 3,000 RPM's, it starts to bog down and starts to backfire.  What could be the cause of this?  In the carbs possibly?  The spark plugs are somewhat black, probably a too rich of a mixture?

Answer
Hello Brett,

  Sorry for the rather large delay in my response. Sounds like it's a fuel problem. My recommendation would be to start with the carbs. Remove them, and take the float bowls off. Clean the carbs internally thoroughly. The main part to pay attention to is the inlet needles and seats. Make sure they are clean and move freely. Other than that, use good plugs and oil. The proper plugs to your machine are NGK BR9EYA gapped at 0.028 in. But, you will notice a much better difference with Champion Powersport plugs. Another thing you could do is turn the carbs air screw in 1/4 of a turn, to lean the mixture out, but only do this if, after checking the carbs, they show up clean. Also, if the sled was raced it may have different jets than the OEM ones. OEM jets for that Cat would be 250 MAIN and 40 PILOT. If you have any trouble let me know. Good luck with the sled! --Arcticatman