I agree that normally lean does that Doug.
But a misfire is a misfire and 9:1 can make the same symptoms.

If he finds mixture does nothing tho that can’t be lean is my thinking.
If totally closed a lean mix will kill just about any engine.

If the idle falls that hard with just the load of the AC, I’d think the carbs are on the lean edge.
Ross brings up using the secondary carb, makes sense but you’d have to make a bracket for it I’d think as the pad on the throttle shaft is different than a generic throttle lever.

As long as you are fabbing parts, makes sense to do it on the driverside and just use it to push the linkage.

Interesting situation, I never considered having to do it. Now I kinda want to make something lol

Would be a bit crowded.
You can always just run a manual choke. If you don’t want the choke plate, leave it, the rod and shaft out.

You can use the fast idle parts from a manual choke without choke plate if desired.

You can also richen carbs if needed, tho that may throw you off elsewhere. 
Make sure your pcv isn’t allowing in a large mass of air.

run two 3310's 780/750's, Drew might have a couple for sale

Kaase bought my inventory of 2x4 780s.

I need to do another batch.
Given the cam specs the OP has given they’d be good if inline mounting is required.
If willing to do sideways, he can use just about anything

Ehhhh just ignore it. He used a bunch of my calibration info years ago and grossly misunderstood it.
He ended up using 76 jets in 2x4 550cfm carbs and his conclusion was that the FE just doesn’t make any power.
Couldn’t be more ignorant.

Either way, killer build.

Totally common with secondaries.
In theory they should shut on their own, in practice not always.
Adjust closing link to be a little tighter.