Thanks, gentlemen (and ladies if any here) for great suggestions. Yes, I first suspected and still suspect fuel to have been bab due to even my tank of saw Stihl MS 261 stalling at idle on the "fresh" fuel I got. I bought definitely fresh 93 fuel with ethanol after that (which pains my heart, but I cannot trust non ethanol station anymore) and I splurged $39.99 for MotoMix (which gave me even more chest pains). I know fuel is not to blame. I know the compression is not to blame. I know the muffler is not to blame because I verified that spark arrestor is clean - which it is, it still has shiny appearance since it is still new. And I tested starting with muffler off completely, so muffler possibility was eliminated. Two carburetors pretty much eliminates carb issue. I also gave one carb extremely good cleaning and testing. I still think I have a massive air leak. The saw died like it ran out of fuel, all the lines are patent and there is plenty of pressure in the tank that builds up almost instantly with cap closed. There is never vacuum there. With pre-carb delivery checked and carb itself cleaned and tested with alternate carb, I think the perfectly running saw stopping inside the cut was likely due to a vacuum leak, because I do not feel vacuum forming when I close the air filter hose with my thumb. I have received Mityvac vacuum and pressure tester, I just need to find time to test pressure and vacuum. How much PSI and how much inHg do I need to pump to safely test seals and gaskets? I think "Married with Engines" You Tube channel has a few videos posted, I need to check how much she pumped hers to.