Allen,
I appreciate and agree with what your analogy of the unvented plastic gas can. I'll admit I was a bit confused on the issue and was certain that it would have to be a vacuum condition as opposed to a positive pressure condition. Carl nailed it with his explanation.
I found this
web site and read through the troubleshooting section. Scroll down about half way down the page to FLOODING(OVERFLOWING).
The carb isn't leaking and all I did was make sure the tank was vented through the cap. All is well that ends well!
Thanks,
