Snowmobile Repair: Olympic 340 works on one cylinder, engine cold, denniskirk

Question
My 1978 Olympic 340 starts on one cylinder only. I have changed the points, condensers, ext coils and HT wires, plugs (BR9HS and tried B8HS with better results). When the engine is cold, the same plug either fouls or gets wet. After the engine warms up and with a new plug in the problem cylinder the sled runs great. Next time I start the engine cold the same thing happens...1 wet plug. It also backfires through the carb a few times now and then when I give it gas. The spark between the HT wire and ground is weak (1\16 in jump and yellow) when the engine is cold. When it's hot I get a good spark (3/8in jump and blue). The timing is right on the mark on the crankcase when my points open with the advance lever fully actuated. I have adjusted the carb floats to well under the specs (lower gas level) to see if it was flooding and I could then get full power when hot. I doubt the int. ign. coil which I have not changed yet. Please help!!

Answer
Hello Harry,

  There is definitely a problem with the ignition, as you mentioned the yellow spark when the sled is cold. Unfortunately, I would have to say the internal ignition coils are probably intermitly producing a weak spark during use of the sled. You can get the coils for cheap here:  http://www.denniskirk.com/jsp/product_catalog/Product.jsp?skuId=20190&store=Main...  If, after replacing the coils you still have trouble, here is what I recommend. Try installing NGK B8HS and putting in jets one size smaller. That should take care of the fouled plug on one cylinder. I hope this helps you. Let me know if you have any other questions. Good luck with the sled! --Arcticatman