Ok, I did some speed reading over the pages of this thread. If I'm asking questions already answered, have some patience.
Item 1:
Has the bike ever run properly with these carbs... that you have witnessed?
Item 2:
Just for clarification, your carbs have idle mixture screws. They are supposed to meter the flow of fuel that is already premixed with air. Air screws directly control the air being mixed with the fuel.
I also have not seen those mix screws that fit flush with the carb body. They all stuck out on the ones I've seen. While that part doesn't really bother me, the part of it that inserts into the carb body does.
For one thing when those screws are lightly seated, the tipp usually protrudes a bit into the carb bore. Can you verify that. The function need here is the ability to totally shut off the fuel flow from the pilot circuit. If, for example, you have the wrong adjustment screws, perhaps that are too short for the function, this would allow more fuel to enter the carb bore than was expected per design. Extract one of those IMS and post a picture and or measure it's over all length. Is it physically long enough to reach the carb bore exit? While you have it out, verify there is an o ring, a washer, and a spring behind that adjustment screw.
Item 3:
I recall a picture that you posted showing the float height adjustment that allowed gravity to compress the float valve spring pins during the measurement. This is not correct. The spring pins must have full extension, the valve tip must be resting in the seat orifice, the float tab must >>just<< touch spring pin, and the bottom portion of the float must be at the proper distance from the carb bowl mount surface. Please verify these components are aligned in this way. FYI, I usually asjust the floats with the carbs on their sides, assuming they are off the bike. But, they don't need to be off the bike to adjust properly, as long as you pay attention the correct parts alignment/orientation.
Item 4:
Also, about the float system. Test for basic operation. With the float bowl off and the carbs fed from the fuel inlet, can you manually work the floats to verify they shut off fuel? When this occurs, are the floats about parallel to the bowl gasket surface?
Item 5:
Assuming you've found no discrepancies above...
Then it is time to move on to the slide needle/mains fuel circuit.
Have you verified that the main emulsion tube pocket in the carb body can get a free flow of air from the air jet?
Have you verified that the slide needle jet orifice is present, unworn, and unaltered?
Have you verified that the main emulsion tube bleed holes are clear?
Have you verified the main jet size is correct and the orifice diameter matches the marking on it?
That's all I can think of right now...
