Hi Tim,
Are we talking the shiny AMAC you've posted elsewhere?
https://www.douglasmotorcycles.net/index.php?topic=9260 Is this the one with the concentric slides? The outer slide (very roughly "throttle") should be attached to the long/lower lever on the double handlebar lever.
Your first photo in this thread looks like a pagan sunrise - it's meant to be a row of 7? small holes, which AMAC refer to as "the sprayer". The jet is submerged and just meters the petrol into a pool underneath the sprayer.
Starting with the assumption that the bike has run in the past and should run again, let's just focus on starting technique.
The AMAC of the period is by no means "automatic", and although we could refer to the lower lever as the throttle and the upper lever as "air" or "mixture" the functions of the two levers are not independent. Sadly you can't rev with the throttle and fine tune with the air.
Things are even more messed up when the engine is cold, particularly with a Douglas because of the long inlet pipes.
Set the magneto lever about half way - tight wire should be advance (faster running).
Make sure there is some oil in the crankcase - say 2 or 3 full pumps from empty.
Start with throttle open 1/4 - 1/3 - 1/2, and the air lever fully closed.
Engine starts? Excellent. If you open wide either lever at this point the engine will stall. Perfectly normal.
1920 engines most often don't go "vroom vroom" in response to the throttle, particularly when cold, so don't try. Instead massage the levers slightly to see if you can keep the engine running for a minute or two. Don't thrash it - aim for a very fast idle. Small changes to the levers is the best bet, almost certainly with the air "more closed" than the throttle. Change the engine speed by moving both levers together. (The air lever is certainly not a choke as found on more modern carbs - it is not designed to be closed for starting and opened wide later.)
See how that goes. Keep in mind that air-cooled engines are not designed to run for long periods while stationary. Use a fan to blow some air on the engine if you're going to run the bike on the stand for a prolonged period.
Cheers
Leon