Stihl 064 gas tank breather?

So, I've had a problem with my 064 AV the last few times out. Runs great for five or ten minutes, then starts to die. Keeps stalling out between cuts, and eventually gets to a point where I can't restart it. No decompression valve on this monster, so restarting a dozen times over is not a minor detail, either.

Suspecting it might be a fuel pick-up issue, I noticed it was always happening when I had used maybe 1/2 the tank of gas. I had it in my head it must be a crack in the fuel pick-up hose, but then today noticed the tank makes a hiss sound when I unscrew the lid. So, when it stalled today, I simply loosened the lid and retightened, and voila! She ran fine again.

Seems I have a problem with pulling a vacuum on the tank, and no make-up air can get in. Who knows where they hide the breather on these tanks? I'm assuming a sintered bronze, like they used on older saws, or has the technology changed?

Check this out, the tube on the left is your vent. Should have an insert in side the end of it.

This might be helpful as well. BTW: Southbound is a member here as well.

http://www.arboristsite.com/chainsaw/128259.htm

Hmm... reading that, I see it's not abnormal to have positive pressure in the tank. Maybe the hiss I hear when I remove the gas cap is pressure, not vacuum! Might have to experiment more with this saw, but I do worry about it running lean at WOT, if the tank isn't venting right.

I'd say your first thought about the fuel line could be the problem. My 029 acted the same when the fuel line had a hole in it.

If the saw runs fine after you crack the cap, then you definitely have vacuum issues in the tank.

Yep... exactly what I was implying. Any concern with it running lean, though? I'd like to run it another day, cracking the cap to see if it fixes the problem after each stall, just to verify this is the problem.

Running again to verify the problem probably won't hurt it.