Snowmobile Repair: 95 polaris xlt 600, polaris xlt 600, air screw

Question
the engine is only running on two cylinders. all 3cylinders have 125 psi of compression. all cylinders have sparkand are getting fuel.the carbs i just cleaned andthe carb on the dead cylinder i took apart twice to check for faults Changed spark plugs,fresh gas ,cylinder in question is the middle cylinder . Any help on this would be appreciated.  

Answer
Hello T,

  This seems to be a very common problem on the older triples. Here is what I would look for. One thing that can cause alot of trouble is a leaking rubber carburetor flange/boot. When they leak, they allow air to get in the cylinder and run rough. To check, start the sled, and spray carburetor cleaner on the boot, to see if it changes. But, I don't think that is what the problem is. It's most probable that the middle cylinder is getting to much fuel and causing the spark plug to not fire. This is generally the problem. Try using Autolite or Champion Powersort sparkplugs, as I would not recommend NGK. Also, try leaning out the air screw on your middle carb, by backing it out half a turn or so. Another thing, sometimes you will get a spark when you take a plug off, but when it is under compression in the engine, it will not spark. You might want to consider taking the coil in for testing. hope this helps, let me know if I can answer any other questions you might have. Good luck! --Arcticatman