Depends on the engine obviously.
I toss the flat head adjuster and install 8-32 brass set screws 1/2 inch long.
Put a drop of purple loctite in them so they stay in place.
This way you can adjust them while the carbs are installed with an allen wrench.
Later carbs take a 10-32
Closed throttle on 2x4’s is a big part of the battle. Exposed t slots lead to rich idles, and often complaints of the same nature.
I change all my secondary units to use set screws. I use a punch on the aluminum boss to tighten up the thread bore. Loctite would be less violent LOL. But a punch works. I just got the two 1850s idling on the 351C. Idle is 1100~1200 which is normal, best vacuum is 11 in/hg. The secondary are right now about 3/5 turn from initial contact. Basically I started with the primaries set to expose just a hair of the transfer slot and the secondaries open 1/2 turn. I backed off the rears 1/8 turn and backed off the primary about 1/2 turn. The adjusting screws are 3/4 out. The idle mix screws are not terribly responsive, I could probably choke down the IFRs a little bit but it "stinks" a bit while idling which is a lean indication, so I'll leave it as-is until I can get the LM1 and laptop on it to get some readings.
