First off I gotta say I'm probably working on the all time high hrs 5100. Used daily to cut firewood year round for 5 yrs.
Saw runs fine off idle but won't idle right. Is real irratic at idle and mostly just dies but will occasionally go lean before it quits. No air leaks that are easy to check for. Rebuilt carb, checked fuel line, impulse line, compression is 170+, muffler is clear, no scours on piston and ring and spark is great. I'm guessing its time to set up for a case vac check. Maybe he has plum wore out the crank bearings and seals.