Snowmobile Repair: Why do i keep fouling plugs, air screw, heat range

Question
I have a Arctic Cat 440 and i keep fouling my plugs why? it has about 5500mi. on it.

Answer
Hello Adam,

  Like I say, spark plugs are the evil of snowmobiles. At some point in time, sleds always foul plugs. Sometimes the plugs will get you half way through the season, sometimes only a day. Here is where to start. Take your carb apart and clean it thoroughly. Use good spark plugs, like NGK.  Also, it may be time for a new coil, if your spark seems a little weak (yellow in color). Plugs foul when there is too much fuel going to them, either because the coil isn't producing a powerful spark, or there is too much fuel coming form the carbs. On the carb, there is a small air screw that goes into the carb at angle. Turn it out  1/2 of a turn on each carb. If all else fails, try a spark plug if higher heat range. For example, if you are using NGK BR9ES plugs now, you would use BR8ES plugs, which are hotter. Hope this helps. Let me know if you need any help. Good luck with the sled! --Arcticatman