sorry I was out the last days.
If your system is as messed up as you descibe you’re probably best advised to first get that car started, just somehow. Then warm up the engine and block off the aux carb completely. Now have the carbs balanced and properly tuned. This is just to get one safe room to begin from …
The aux carb is often described as not serviceable and the Parts catalogue lists it only as a single part (1K 04L). The only thing you’re supposed to service is the AED filter (19.15.43), the gaskets, the needle valve (19.15.42), the diaphragm (19.15.40) and the spring. You seem to be well into that routine.
The internals of the aux carb are virtually untouchable. No people I’ve talked with about the AED conversion ever had any issues about the lower part of the aux part except for the routine maintenance parts mentioned. Chances are that even the GWC (Garage without a clue) hasn’t managed to mess anything up in the internals of the lower part of the aux carb.
I enclose the mounting instructions. It is just your mentioning of the “mixture adjusting screw” that confuses me - there isn’t any on the aux carb. Mixture is all controlled - originally by a bimetallic strip and following the conversion - by the positioning of the two cams and the size of the gaps.
Last caveat: the conversion kit expressly recommends to let the cams’ position on the shaft unaltered. Your GWC might have ignored that advice.
75 XJ6L 4.2 auto (UK spec)