Whats my next step for solving my light-throttle surge?

Awhile ago when I first installed my Carter AVS, I had an off-the-line stumble that ended up being mostly solved by going back to the original rubber accelerator pump.

I'm still having a problem with a very light throttle surge at very low RPM, with the rpm audibly wavering up and down just a bit unless I give it more gas when cruising at around 25-35. Today I tried opening up the idle mixture screws another 3/4 turn each and it didn't make a difference. Before I sent my whole dizzy off to FBO I tried fiddling with the vacuum advance and it didn't really change anything.

I've read some people recommend a couple of small holes in the throttle blades to allow the idle circuit to work better - would this be a good thing to try it if seems to be free of any misbehavior everywhere else in the driving range? If I try getting the engine warm and then turning down the idle as far as can in drive and it seems better, might this be a solution?

I've also read about drilling out the idle compensators, but I don't want to go buying a set of wee drill bits and yet another gasket set for this thing if I can do something simpler first.

Was everything good before changing the carb? Any other changes whatsoever? What engine?

Yes, this only happened after changing the carb. This is for my 318 wagon in my sig.

Are you running vacuum advance? If so try disconecting the hose from the distributor(plug hose so no vacuum leak) and test drive. Sometimes too much advance will cause a surge. If this cures the surge you may be able to adjust the vacuum advance with a allen wrench.

You are lean....

I agree lean and to fix this properly you need some smaller diameter metering rods.

Assuming timing & fuel pressure are good, no restrictions in fuel lines:
Metering rods as HemiRick says
More jet
Less timing

Couldn't I be lean in just the idle circuit though? This doesn't happen unless I'm just within the first crack of the throttle to maintain speed on a slight grade in town. Everywhere else it doesn't stumble or surge at all.

enlarge the idle feed tube orifice in the primary clusters.

If the jetting is correct, try a different step-up spring.

last time my dart did that it was because it was lean on the primary side of the carb. i ended up going two sizes fatter on the primaries and it straightened right out. only thing i changed at the time was the exhaust system.

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Couldn't I be lean in just the idle circuit though? This doesn't happen unless I'm just within the first crack of the throttle to maintain speed on a slight grade in town. Everywhere else it doesn't stumble or surge at all.

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Since you are driving down the road when it's happening, the carburetor is now using the primary jetting. Try going one step larger on the primary jets and the lean surge should go away.