Chainsaw Repair

Have you replaced the crank seals and/or done a vac/pres test?  Leaking crank seals can cause the saw to have a weak impulse signal at idle.   That'd cause the pump section of the carb to be weak....................which will allow it to lean out at idle as you describe. 

Seen that several times with Poulan Micros with old crank seals (that seemed to run fine otherwise).  That's a saw series with a 15 mile long fuel line that NEEDS a healthy carb pump section (and a healthy impulse signal).