holley 1920 carb question

Well like I said, it is definitely a carb issue and not a vacuum leak such as an intake gasket leak or carb gasket leak as both the problems get solved by swapping out the carbs.....I am going to try a new air mixture idle screw in the one that won't idle and see what happens.....As this is the one that starts great , even when hot.....It doesn't even turn one revolution when hot or cold and it fires right up strong....As far as the one that idles great but won't start hot, I do have the charcoal canister on it and the bowl vent line is connected to it.... Your quote as follows

"The second one that will actually idle sounds to me like it is not "venting" after it sits and heat soaks. In other words, the gas vapors that accumulate in the float bowl because of fuel perc have nowhere to go, so they hang around and get sucked into the intake when you try to start it, causing an overrich mixture until the engine pulls enough fresh air in.

If you are referring the '72 in your sig, there should be a metal or plastic nipple on the top front of the carb where the hose to the charcoal canister connects. Adjacent to that is a lever that acts on a small valve that permits fuel vapor to flow to the charcoal canister at closed throttle but not otherwise.

You can't plug that hose up. That'll cause the situation I just described. If you still have the canister, make sure it's connected properly. If no canister, then just run a length of line from the carb to a spot where the excess vapor and possible miniscule traces of fuel can safely exit."

Yes, it is a 72 dart...has factory charcoal canister....bowl vent hooked up and bowl vent valve is working properly.....I hooked it up exactly as the carburetor that starts great when it is hot does.....That is why I know it is something in the carb itself....The routing of the hoses is exactly the same....I am stumped