Stihl 024AV won't run long
My used Stihl 024AV chain saw has developed the problem of quitting after only a few cuts, and then I can't get it started again for a while (usually I leave it sit for a day). This is a recent development - the saw ran as long as I wanted it to when I first got it. I am suspecting that the problem may be that the gas tank air inlet vent is clogged. Since there is no vent in the gas cap I surmise that the tank has a vent hose fitted, but I don't know where it is. I have a manual for the 026 model, but nowhere in the manual does it show where the gas tank vent is. Can anyone point me in the right direction?
Also, I note that there is a round rubber "button" on the top of the saw above the name plate on the left side. The "button" has a screw head in it which I can loosen but which will not come off. What is this?