Snowmobile Repair: Problems getting AC 91 EXT 550 Special to idle at 2000-2300rpm, air screws, piston valves

Question
After at least 6 attempts to re-tune carbs and to set idle on an 1991 AC EXT spec 550. I can't seem to get it to idle. I completely cleaned carbs, jets, bowl, everything. followed the book about adjusting choke 1st, loosend throttle cables, set idle screws 1.5 turns further after it touched piston valves, adjusted throttle cables until slack is out, set air screws 1 turn from seated position. The sled starts on first pull. but barely idles at 1000 rpm. I turned idle screws clockwise(tightened) it helped bring up idle enough so it won't die butscrews are almost totally tight, but when you excellerate it boogs out (to much fuel?) I tweeked the air screws a bit either 1/4 turn in and out.. nothing seems to help..what am I missing? thanks for any help...

Answer
Hello PW,

  There are basically two possibilities. Either a small air leak, or an ignition problem. To check for an air leak start the engine, and before it gets warm, spray carburetor cleaner on the clutch end of the shaft, where the crank seals are. Also, spray where ever there are gaskets. If the idle speed changes when you spray, then you have an air leak. Now, for the ignition, be sure to use NGK BR9ES gapped at 0.028  You may want to consider, removing the coil and CDI and having them tested at your local dealers for testing, it should cost close to nothing. Fouled spark plugs are a very good possibility. Hope this helps you out! Take a look at my new site, www.freewebs.com/thesledzone/ . Good luck with the Cat, let me know if I can help with any other questions at all! --Arcticatman