Mercruiser dual 1 barrel Rochester (7025183 BC and 7025184 B). These were used on mid 60's I6 engines. The following year ~ 1965, Mercruiser changed to the small bore Rochester 2GC. I don't know the reason for it but I can make a guess.
I've read that some of the reasoning behind multiple carburetors, for 50's car manufacturers, is that you could tweak out a little more RPM/horsepower, using the previous year(s) engine, to give marketing leverage against the competition. It had nothing to do with making the car more reliable or easier to maintain.
"Adding CFM to a truck will only help at engine speeds you don't want to use." "I found there was nothing to gain beyond 400 CFM."
