THANK YOU Big Block
That explained it perfectly.....It didn't seem like a choke, because it only seemed open when it's warm, and why would you choke a warm engine. I've seen the same sort of thing on a couple Packards here, but it was always deactivated for some reason...usually with a hand choke added under the dash or somewhere. The intake and exhaust runners are actually fastened with shared bolts. That incharge is WARM.
Too many of these old engines are going away. These old guys want Vette power in everything, and this one's no exception....everytime he comes to visit it he makes a comment about a LS3 swap. I have a perfectly lovely straight eight out of the Packard roadster he ruined two years ago....sitting in my garage. I'll take this boat-anchor six and store it out there too...when the time comes.
***This arrangement looks NOTHING like anything from a mustang... Flapper, spring, and Sheetmetal box up around the carb. It actually looks homemade.....it belongs with the oil bath air cleaners and swamp cooler A/C. Fred Flintstone tech.