I have a 80 K-5 that I have done complete body off rebuild on. Stats are a 383, sm465, np205, detroit locked 12 bolt, with honestly too many extras to list. My problem is that if the truck sits for more than two days it becomes very difficult to start. I will have to crank it over for at least 35 seconds for it to fire up. This is strange because if I crank it up any other time within that day it fires up as advertised without even cranking a full revolution. I think that the fuel bowl is emptying while it is sitting still. The carb is a 1903 Q-jet(new), holley electric fuel pump(new), -6 braided line from the newly sealed fuel tank all the way to the carb. I installed a "one way" check valve(new) to ensure that gas doesn't leak backwards when shut down. Also I let the pump run through the line to pressurize it before the key is turned to crank the engine. The ignition is a MSD 6-AL. I called Edlebrock's tech line and they said to check the bowl seals under the throttle plate for leaking. I did even though it is new and found no problem (i epoxy'ed them anyway and know that they don't leak). I'm a little stumped about this, because everything is new and runs very strong. It just is difficult to start after a few days of not running. I would love some advice from anyone who has any no matter how strange it sounds. It's kinda embarrasing to have my newly finished project have this problem.