What do you think of this plug?

Are you using a wide band or just tuning by the plugs? Have you reduced the main jets to lean it out up top? What did it do to the cruise? You mentioned at one point you had a lean surge, are the carbs four corner idle? Is there another idle speed screw on the secondary's?

I highly recommend some type of recording wide band, it's a wonderful tool for carb tuning.

My advice would be to reach out to Dom.