Toivo,
Thanks so much for the reply and pictures. That set-up looks very similar to mine. It is a little difficult to see the linkage but I think I see the same slot on your linkage, on the arm to the rear "carb". It appears when the bellcrank rotates it would begin to advance the front carb first, then after 10 or so degrees of rotation the play in the slot would be taken up, and the rear would begin to advance. Because the moment arm on the bellcrank is of different lengths for each carb linkage arm, full throttle could be adjusted to be reached simultaneously. It is this apparent progression between carbs that has me confused.
Thanks again for your time and pictures, Steve