Hi, thanks also for your posting - this way I know I am not alone with this misterious problem.

First of all, I don't think it is fuel. Bad old fuel smells strong. I had emptied my tank, relpaced the fuel and the problem was still there. I also checked the sending unit in the gas tank. My tank also does not show any sings of rust or dirt.
Steve, you carb / choke idea is great. My engine actually dies usually somewhat like under choke. After having checked the choke several times, I can say this is not the problem.

Anyhow, in the meantime after doing lots of fuelrealted work and not finding the problem, I am starting to believe that it could be an electrical problem. Ignition system. Just recently a guy told me that an electronic ignition had solved his stalling problem years ago and for good.

The only reason why I will keep on going through more fuel related stuff is the fact that I always was able to restart the engine and also to keep it alive through the choke and power lever. I also strongly believe that the problem is heat related. Robert Hess gave me the advise to check the fuel lines for vapor locks.
The fuel tank venting line and the opening is somethng else to check. Mine was ok, in your caseit could be the problem.

Let's stay in touch on this!
Christian