Back "then", the bowl vent was suspected to be needed to properly vent the float bowl in ANY weather, when the bowl was already vented into the area inside the air cleaner "ring", usually. On Holleys, especially on the primary side. AND, the bowl vent closed as the throttle was opened.
On Holley 4bbls, the basic casting for the bowl vent was still there, if not machined, in the earlier '70s, when the bowl was then vented into the carbon canister. It was deleted due to further control of evap emissions. In the middle '80s, the 318s (as did many Chevy V-8s) had an additional flap in the air cleaner to keep any evap emissions INSIDE the air cleaner when the engine was stopped. "Absorbed" by the normal carbon canister AND the one located in the air cleaner body, just inside of the air filter element.
In the later '60s and such, I did many considerations of why Chryslers tended to have a "hot soak" start issue in the hot summer months, but found they were doing nothing different than Ford or GM was doing with their carbs or engines, that I could determine conclusively. ALL had external bowl vents that were open at idle.
GM had their aluminum-sheet "heat shields" for the 4bbl carbs. They just shielded the carb from heat radiated upward from the intake manifold. If that temp also affected ambient temps around the car, they just delayed the heating of the carb's float bowl fuel. The ONE thing which Chryslers usually had was open air around the carb, as Ford and some GMs tended to later hide the carb from air flow around the carb. The Rochester Q-Jet had a small float bowl, so if it fuel percolation losses, it'd refill quickly. VERY small compared to other carbs of that time.
GM's observed issues were with the starters getting hot from nearby heat sources, affecting the starter solenoids, which generated a variety of heat shields for the starter solenoids. In some cases on the motorhome chassis vehicles, a TSB for conversion to a Ford-style solenoid set-up was issued. I think I'd rather have an extended crank time rather than a starter that wouldn't engage.
FEW engines started quickly back then, although there were some that did, although it seems that some were worse than others. Still, storied of engines that started "with a touch of the key".
SO, best "fix" was to follow the Chrysler-advised starting technique of "1/3 throttle" accel pedal position during starts. IF there was a fuel percolation issue, or an accumulation of fuel vapor in the carb throttle bores, that'd clear it out sooner than if trying to start the engine with a closed throttle situation. The other thing was to make sure the battery, ignition, and charging systems was in good condition and the spark plugs were gapped at .035-0.040".
Some of the Holley 4160s and other 4bbls of the l60s era had a "hot idle compensator" to add a little air into the throttle bore to prevent an over-rich idle situation. I had a Holley with one on my '67 Newport (in the middle '80s). I adjusted the bi-metal spring to keep it closed or slightly open, with no difference in performance. Might have been that it wasn't hot enough to really need it?
Whether Carter AFB (OEM), Holley 4160, or TQuad, they all seemed to start the same for me on the '67 Newport 383. Even as our fuels migrated more toward E10, or before. But to me, the extended crank time was a real non-issue from what we had on the '66 Newport 383 2bbl (when it was a year old and later). Use the throttle position during cranking that makes the engine start the quickest, which should be done no matter whose engine or carb it is--period. Once I stopped (somewhat) obsessing with it, it became more of a "normal deal" to me. A seeming quirk of owning/driving a Chrysler. As always, I trust Chrysler engineering more than I do Ford and especially GM. In ANY event, some things aren't worth "fighting" so you learn to best live with them as best you can!
ALL of this was taking place in N TX, where the summers were usually 90+ degrees F for weeks on end. And in a time when ethanol was used sparingly for an octane enhancer rather than an oxygenate in the fuel recipe.
Enjoy!
CBODY67