Strange Weber IDF problem - loss of main circuit?

[Geoff2]

What spark plugs are you using?

[Nut124]

What spark plugs are you using?

NGK PBR7ES. Was running PBR6, but they were running almost white, lite grey even thoug running a bit rich.

https://www.ngk.com/heat-range-conversion-chart-2

Heat Range Cross Reference Chart
NGK PULSTAR DENSO CHAMPION BOSCH
2 9 18, 19 10
4 1 14 14, 16 9
5 1 16 11, 12 8
6 1 20 9, 10 6, 7
7 1 22 7, 8 5
8 2 24 6, 61, 63 4
9 2 27 4, 59 3
9.5 2 29 57
10 2 31 55 2

Now I'm wondering if there is a chunk of rubber or dirt in the carb bowl that blocks a main jet, but does not stick to the jet. Thinking about using a vac pump to remove fuel from bowls via the emulsion well, multiple times, then examining the captured fuel for dirt.

[Nut124]

Suctioned the float bowls via the eTube well.

I wonder if this is the culprit: The FWD carb had lead and some kind of plastic debris in the bowl:

The rear carb was clean.

[Geoff2]

'7' heat range is the range stated in my NGK catalog.

Metal pieces might cause strange problems...like you are having.

[Nut124]

It seems that the problem is solved. Apparently, the lead spec worked it's way to the bottom of the eTube well. It would then get sucked up to the main jet under WOT, high fuel flow. Sometimes it would fall down, sometimes it would not.

I do think I had some flooding related to the excessive float drop setting earlier. That has now been fixed as well per advise from a reply here. Plus I now have a completely new or rebuilt ignition.

[MadBill]

... Plus I now have a completely new or rebuilt ignition.

And an extensive collection of spares, courtesy of all the parts that you changed before nailing the culprit...

[V12MECH]

Congrats to you for being so through, we all have "spares" from trying to solve a problem, goes with the obsession.