Snowmobile Repair: 1987 Polaris Indy Trail (one cylinder fouling), mikuni carb kits, speed changes

Question
I recently purchased an 87 Indy Trail the carbs were gummed up with the floats stuck (fuel blowing out of overflow port) I cleaned all parts reassembled and she started right up. After warm up the idle was a bit high and didnt respond to any idle adjustments down, then after riding for a short time (two minutes) it lost all power in the upper end and the left hand plug came out all wet and oily / black at tip. The right hand plug looks fine a light tan appearance.It wont go over 4000 rpm without bogging down, and every time its the same left cylinder/plug/ carb. I also did a by feel carb plunger synch and the valves move very close to simultaneously.

I am familiar with the history and use of the use of the machine and it was always maintained but this past seasons layup left unstabilized fuel in the carbs.

 Do you think it needs a complete carb rebuild or is it possible the choke is allowing too much fuel by on the one side any help greatly appreciated.....I hate to miss the great spring sledding......thanks  Bo  

Answer
Hello Bo,

   Two things are very possible. One would be that the seals are worn on the crank. To check them, spray carb cleaner all over behind the clutch where the shaft exits the engine. Do thus procedure with the engine running. If the idle speed changes, the sled needs new seals. Other than that, my recommendation would be to install new main and pilot jets, as well as a carb kit. It has been my experience, that only Mikuni carb kits work well for the most part. There are others, and they work decently also. you can get parts for the sled at www.mfgsupply.com , www.ronnies.com , and www.denniskirk.com . After rebuilding the carbs, you may want to use STP in the tank for a little while. It works well in the sleds, especially after a carb rebuild. I hope this helps you. Let me know if you have any other questions. Good luck with the sled! --Arcticatman