Small Engines (Lawn Mowers, etc.): McCullough stalls on me., chainsaw running lean

Question
I've got a McCullough Mark 1 Frontier chainsaw.  At first I noticed the idling remained too high, and then it would not idle at all, but stall.  I cleaned the air filter, took the carburator apart, cleaned everything out, also the filter at the fuel pickup. Right now, it would start but run only on peak revs. It runs even and cut perfect, on peak revs, but the moment it slows down it quit right away. What else could be wrong.
Thank you for your time.

Answer
This may be a tough one to isolate without some specific tools.  It sounds as if the engine may be overly lean.  You don't want to run a 2-stroke lean, you'll ruin the engine.  Overly rich could cause a similar syptom, but you should notice the plug fouling quickly and being oily.  If the plug is fresh and not fouling or oily I'd start by looking for leaks.

If it is lean, then it sounds like you may have an air leak somewhere.  These are very difficult to locate without the proper block-off plates and vacuum and pressure testers.  Often the leak is in the intake gasket/manifold.  Sometimes it's the carburetor itself.  You can have a fuel line with a tiny hole.  You may also have a problem with a crank seal.

You could also have a carburetor problem that you missed when you took it apart.  I use an ultra-sonic cleaner for cleaning carbs.  I find this is the best way to get into the tiny passages and knock the dirt loose.  The next best way is to soak the carb in a cleaning solution for an hour or more.  The carb vats that you find at the auto parts stores work well.  Then reassemble with a new kit.  In my shop, we always replace the fuel lines and filter and rinse out the tank.  Especially with chainsaws.

Without the tools needed to do crankcase pressure and vacuum tests, I would start by going through the carburetor as I detailed.  It's very important to replace all gaskets and make sure that all seals are tight.  The most common major problem on 2-strokes I see in the shop is with cylinder and ring failures due to overly lean or overly rich fuel mixtures.  

Finding a problem like this requires some diagnosing and testing.  So it may be an elusive problem.