Hi AK260,
Blodi and I tried for over a year to address the AF dip once you get into the throttle. You can see the pain, suffering, blood, sweat and tears in this thread. https://www.classiczcars.com/forums/topic/56375-weber-selection-and-initial-jet-tuning/#comments We tried many etubes and completely disabled circuits but no significant changes to the rich dip were observed.
The experiment still is not over however, it is interesting that you also see this on single circuit SU's and we see it on 5 circuit DCOE's. There is also a video of chaps down-under tuning a Z with DCOEs and then with EFI and they get the same rich dip. I did some digging and a fellow who tunes bikes had the same problem and found it to be caused by the exhaust system.
Our recent thoughts for addressing this are:
1. Putting tuning reflective points in the exhaust
2. Putting anti-reversion traps in the manifold
3. Adjusting the mechanical cam timing with the 3 points on the cam sprocket
If you have no luck shaping the needles, I would be grateful if you did some runs for each of the 3 cam settings to see if A/F changes in this rich area. It may possibly be tamed by valve timing as we have these odd non-cross-flow heads.
Again, great work! Very impressive.