grasshopperlegs
Marksman
It sounds like a you have a some dirt in the vent hole in the oil tank. It can be in front of the saw near the muffler or even near the bar oiler hole. I worked for a Sthil dealer and what I would do is clean the oil tank real good. ( When you put oil in the tank make sure there is no saw dust on the rim of the hole or it will go in the oil tank.) So after you clean the whole tank out then put a little air pressure in the tank by maybe using a rag to get it somewhat air tight. This worked for me many times. Hope that helped.