The intake manifolds on many older saws include provision for routing crankcase impulse to the carb. See pic of intake manifold from an Olympyk 480 Super. The gasket that comes with genuine and non genuine Tillotson carb rebuild kits does not maintain the integrity of the routing for the crankcase impulse. See second pic of manifold with kit gasket. I went round and round trying to remedy an old saw not starting when warm unless choked, surging at idle, even accelerating from idle with no throttle applied and failing to accelerate when triggered to. All low-speed circuit issues. The fix was easy and absolute with a hand made gasket using bulk material from an auto parts store.