I have 454 in my Suburban with a newer Edelbrock Carb. Before the Edelbrock, I had a Carter AFB. Both these carbs ran excellent on the other motors they were on (they would fire right up after sitting). Both carbs on this motor act the same way. It just takes forever to fire, especially after sitting over a couple days. Could it be the fuel pump allowing the fuel to leak back down from the carb?