Snowmobile Repair: dead cylinder., crankshaft seal, exhaust stroke

Question
I'm helping my brother with his mid 90's ElTigre 5000.  He has a dead cyl. I am a licensed journeyman auto mech but have little experience with 2 strokes.  I've gone through the usual suspects, check for ignition, check for fuel and checked for compression and have all of the above.  Plugs are new and the one on the dead cyl comes out absolutely clean and hardly noticeable wet and only a faint odor of fuel.  I do know that air fuel mix  is pressurized in the crankcase by the downward exhaust stroke and as such crankshaft seal failures can result in dead cylinders, but is there a method of positively testing for this and/or is there something else I should be checking at this point?
Thanks,
Steve G.

Answer
Hello Steve,

  Sorry for the large delay in my response. Seeing how you have compression ans spark, there is two things left to check. To me, it appears to be a fuel delivery problem. In this case, you would need to dissasemble the carb, and clean it. What has probably happened is, a stuck inlet needle in the float bowl. It is possible to have a leaking seal. To check for a leaking seal, you will need start the sled and warm it up for a max of 5 mins. Then, spray cab cleaner on the PTO end of the shaft, all over (behind the drive clutch). If the engines RPM changes, the seal is worn. If you want to make certain it is the seals, or if the dead cylinder is on the MAG side of the engine, you can use a pressure tester such as the one pictured here, which is very accurate;  http://www.swedetechracingengines.com/parts_accessories/pressure-tester.html  .  Hope this helps you. Let me know if you have any other questions. Good luck with the sled! --Arcticatman