Berger could very well be dead right - I know diddly squat about those carbs, only ever having used Monoblocs on my own A. If there are loadsa sparks . . . the carb has to be well in the frame.
Process of elimination, one thing only at a time, and I'm sure we'll know soon enough!
In the course of a long steamy day of riding in rain (am) humidity (all day) and high heat (pm) yesterday, with about 30 like-minded people who should know better but won't grow up, we had several failures which stretched our meagre support vehicle capacity. Ignition issues, mostly. I put it down to lack of use during the covid thing, despite normal amounts of fettling according to the owners. Just glad not to have been of their number myself, it's probably overdue . . .