Oh, gotcha. Okay, that makes sense and would explain a lot.

My last question would be:

If I created a vacuum in the tank due to capping off it's inlet, wouldn't removing the gas cap immediately relieve it? Why would it take a half hour to an hour for the pump to pull any more fuel from the tank? Excess pressure still in the line from the tank to pump? Pump temporarily over exerted?

Just like to understand these systems 100%.