Originally Posted by mr950

If your runnign a Q-Jet, check for a leaking welch plug on bottom of carb. It lets the fuel bowl drain overnight, hence the cold start problem. With the engine off,after overnight not running, look down carb and hit the gas a few times. Is there a pump shot? If not, I'm pretty sure you have a welch plug leaker. Remove carb and clean with carb cleaner, then apply J.B. weld to the leaking plug. Smear it all around the plug[usually soft alum, or brass plug] they block off machining passages on the carb body. Let dry overnight then install the carb , fill the float bowl, this can be done thru the vent tube or cranking engine. Let it set till cold start again and see what ya get. I've done hundreds of these over the years of working on G.M carbs[Q-Jet} Good carbs, you just have to have a handle on them. Heck, my engine builder runs one on a D/stock 396 Camaro and runs 9.40@143 !!!