So I did some searching but couldnt find an answer.
Is there a base setting for the Idle trim circuit on the AFM?
Do you start tuning with it set all the way lean & only richen as necessary, or should it be set in the middle of is range at start?

Starting from 0
Static time
Crack the TB idle screw
Warm the eng. till close of the AAR
Adj idle at TB
Adjust timing
Fine tune idle with trim screw.

AFM idle circuit is just an air bypass screw. Manual says you’re looking for 2-3% CO when fully warm at idle. You are correct that the AFM trim and TB idle screw play off each other. But you shouldn’t mess with the AFM screw without a CO meter or a wide band Lambda sensor.

@wonkipop posted this link a while back and I thought it was a good read:
http://www.itinerant-air-cooled.com/viewtopic.php?t=7761

When adjusting CO you can also see the spec which is stated as less than or equal to on the emissions control label. You will need a CO meter or gas analyzer to set CO at idle.

The answer to my Q:

2056 Ljet with 50mm Vanagon throttle body. Just read the article on Ljet adjustment. I turned the large wheel CCW 4 teeth to get a reading of 13.2-13.4 Plugs look like this:Click to view attachment

Good reference info!

missed this thread.
@Van B has already linked the info mother lode.

other little detail.
you are supposed to pull out the hose from the charcoal can at the air cleaner (assuming there is a canister still there).

......for whatever reason CO on a 75 L Jet is much lower than a 74.
0.2 to 1.2% instead of 2-3% on a 74. from factory manual. measurement is before the cat in the cal models and 75 rest of USA did not have a cat. there was a test connection port on the first muffler for those cars.
as to why and how a 75 required the much lower CO i dunno. logic tells me that would be so after the cat - thats what a cat does? - but the reading is before the cat.
there was a different ECU.

since i have a 74 i have never thought further about it.