75 Dart Swinger / 1945 carb

I recently purchased a 1945 and installed it. It works beautifully 90% of the time. It operates better than any carb I have had since I owned the car (over 3 years now). There is one problem that occurs under a certain set of circumstances.
If I start her up for the day and drive her she drives great. No issues. Idles smooth, drives smooth, shifts smooth, responds great.
But if I have been driving for 20 minutes or so - or if it's especially hot out and I stop at lights (especially long lights) she will start to idle a little rough and then die. Always when I am at a full stop. Never at any other time.
I asked /6Dan about maybe putting in a purge valve since mine was made with a port that was not a perfect solution for opening closing off the purge line. My thought was maybe that was causing it. He said to plug off the purge port first to see if that made a difference. Today I drove to work (about a 25 minute drive) with the purge port capped and she made it all the way without stalling but a few times she started to idle slightly rough and I thought she would stall but it never stalled. I am posting about this for any all input on ideas as to what could be the problem. Idle is set to spec and timing was done not that long ago and seems fine. As I said, most of the time she runs really well. Thanks

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When did you last set the valves?

......time to do it again.

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Yeah....Im the one who destroyed this rare, vintage automobile.....