Carter Thermoquads ~ 'More General Information'

you are confusing the 72-up carb design, with the earlier CS design. they are not the same.

the 72-up carbs merely have a hole in the lid for metering rod guide, that is above float level, that's only more bowl venting. the metering rod passes through empty space and through the fuel in the bowl, into the jet in floor of bowl.

the CS carbs have the metering rod going directly into main well, attached to the lid. the jet isn't in the floor of the bowl, it's upside down on stanchion, screwed directly onto the bottom of the main well. the metering rod is actually inside the main well. the space around the metering rod is therefore more air bleed. the metering rod doesn't just go through empty air space above fuel level in the bowl, like on a 72-up carb. the dedicated high speed air bleed is alongside this tower, and it bleeds more air into the main metering circuit downstream from the jet/rod.

That gap between the metering rod and bushed guide in lid on the CS carb, tiny as it may be, is still more air bleed, in addition to the dedicated main metering high speed air bleed that's already in the lid. It's splitting hairs but I'm including it anyway- because it's there. It's a critical area, that's why the designers bushed it for tight clearance on the CS carbs. It was not critical on the 72-up carbs.

the idle circuit on a CS carb has its own idle jet and idle well, taking fuel directly from bottom of the bowl, separated from the main jet/main well. it has only one idle air bleed on the lid top, not 2 like the 72-up carb.

looking at bottom of stanchion in pics above, that small brass plug next to the main jet facing downward same direction as main jet, that is the separate dedicated idle well- the idle jet is on opposite side surface of stanchion- the idle air bleed is at top on lid, that angled backward tube in cavity in the corner. the main jet when screwed in, seats itself against the nose of the main well. the idle fuel is drawn into the idle jet, around the cavity surrounding the jet/idle well nose, and out the other side of stanchion, into the idle well, then up the idle well to top. the 2 circuits are separated, just in close proximity to each other.