Gas tank venting

I am do some maintenance on a 34-year old Stihl 011AVT. In replacing the gas tank vent rubber tubing (it had started to crumble apart), I found, inside the tubing, a very small fully threaded brass screw. Does anyone know what the screw is for? To my way of thinking, the screw would seem to block most of, if not all, of the air, thus defeating the whole purpose of the gas tank venting system.
Thank you for your help.

It is a very simplistic way of allowing air back into the tank to replace used fuel and stop fuel exiting the tank when the saw is orientated to the side.
Similar can be recreated with Tygon type fuel line and the original grub screws to form a replacement, the trick is finding line the same outer (to seal the tank entry point) and inner that allows air to pass the threads- without forming a complete seal.
It is also VERY important to simply push fit the screws into the tube, do NOT thread them. If you screw them in, the threads cut the inner face and form a tighter seal.

There is a small diameter one-piece brass tube nipple where one end is located inside the gas tank at the very top, and it's curved facing upward. The other portion of the brass nipple goes through the gas tank housing and ends inside the carburetor housing. That's where I found the original, but damaged, flexible tubing that needs replacement, and inside that crumbled tubing was where i found the grub screw. I've located a source for a new piece of Tygon-type tubing. So last question is: I can only see a part of the original flexible vent tubing inside the carburetor housing. Where does the end of that vent tubing go?
Thank you for your help.

It is kind of complicated to explain- not sure if I have an 011 to show you- but in the corner of the air box the carb is in there is a hole that has foam in it- the vent hose terminated in that foam and later models had a fuel filter at the end of the vent hose laying on the floor of the air box.

The simplest fix for you is a short length of fuel line off the barb into the air box and push an Echo style breather into that- job done.

Thank you for your help!

GIBSAW said:

Thank you for your help!

Click to expand...

I did manage to find an 012 at home. Same set up with the vent.



Screwdriver shaft pointing to the foam inset in bottom of the airbox.