Small Engines (Lawn Mowers, etc.): chainsaw dies, engine crankcase, air leaks

Question
My father has an older craftsman which is actually a echo cs451vl with a tillitson carb.  It starting acting up so he has taken the carb apart and cleaned twice and put a carb kit in it.  He said he also checked the fuel line and filter.  It will start, with some trouble, and run at high idle, but when you turn the idle down it will die.  We also adjusted and checked points and made sure stop switch was working correctly.  It still sounds like carb trouble, but what should we be looking for?  Air leak?  Thanks for any help.

Answer
It could be an air leak or a clogged muffler or exhaust port.

When rebuilding the carb did you download the service manual and check the carb inlet metering arm height?  This is like setting the float level on a float style carb.  A little off will usually not hurt but way too high or low will cause problems.

Do you have any way to pressurize the engine crankcase to check for air leaks?

Eric