Your shelf of carburetors reminds me of going to the Portland OR. Swap meet many years ago when there was nothing but neat stuff to see and buy...If the vacuum hose was plugged into the side of the metering block, as in a ported source, I'm with 1980RS, your primary throttle is into the port just above the throttle plate.
If you are on manifold vacuum, and not over activating the primary trans slots, chances are you may in fact be a little on the rich side, and the extra air leans out and brings the idle afr's in check, so, the engine is not labouring as much and picks up rpm naturally, and that in itself picks up some timing centrifugally, and that pick's up more RPM.
In my opinion, get the primary and secondaries adjusted before you go drill some holes in those plates, that's the last thing to do, and more often than not it points to other underlying issues. I get some of these carbs in with holes in the butterfly's, they do not need them 90% of the time, heck, I take out the original ones with holes and put solids in.....and wow, things get better LOL.
To be really straight up forward, getting the idle mix screws "perfect" is not a walk in the park sometimes, 2 corner or 4 corner, and I'm on the pump every weekend, and soon to be at the track. Every one of these carbs I built are different going out the door, if you have a "tuners" secret, I'm all ears !!!! heck I'll pay for it LOL.
This is my "completed" carb waiting shelf.....always looking for tips.
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Your shelf of carburetors reminds me of going to the Portland OR. Swap meet many years ago when there was nothing but neat stuff to see and buy...
Last time I went, probably 13 years ago, it was ALL junk and " model cars".....