Hi, I have fixed many saws with this same issue. Without actually viewing the saw in person, it sounds like an air leak in the crankcase, possible due to old brittle and shrunken crankshaft bearing seals or could also be the join between the top and bottom of the case is warped and leaking air. Either of these conditions or both will prevent air/fuel mixture from being drawn from the carb throat as it is sucking air from the leaks instead. An easy test is to simply put some cellophane plastic (Cling wrap) on the carby inlet and put a rubber band around it to seal it tight. Then pull the starter fast several times and get a friend to check to see if it is sucking in the plastic as you are pulling the starter, which it should if the seals are all good. If it doesn't, it means a comnplete strip down to replace seals and reseal the join between bottom and top of the case. Hope that helps
