You are right, the service manual has little valid info on what you are looking for. In reading, it refers the carbs having a wire that retards the distributor.
found this on page 14-51, and sure you already seen it.
These five AVS carburetors are equipped with a distributor
ground switch, which retards the distributor
when the carburetor is at idle, for better emission
control. The idle speed solenoid which is mounted on
these carburetors, (Fig. 21) is used to maintain a higher