I had a similar problem as you are describing and assumed incorrectly that it was another ruptured accelerator pump. Once I got the truck home, I cracked the fuel line fitting on the carburetor and fuel sprayed out like a fire hose. I hurried up and tightened it back up. I then removed the brand new gas cap and it flew out of my hand from the excess tank pressure. I drilled a small hole in the bottom of the gas cap to make it as original, and that solved my problem.
I am guessing that the excess tank pressure was forcing fuel past the needle and seat in the fuel bowl, causing the excess fuel to make its way into the intake after shutdown.
