The official Ford nomenclature was, Distributor modulator valve. The purpose of the distributor modulator system was to help reduce carbon monoxide and hydrocarbons. The system was designed to use carburetor venturi vacuum to reduce engine emissions. This was done by controlling distributor spark advance. Ford engineers felt that a retarded spark provided a hotter combustion chamber and exhaust manifold temperatures that caused more complete burning of the fuel. Another early form of emissions controls as the Government tightened their control over the auto manufactures. Surprised that your's is still as complete as it is. A lot of those ended in the junk piles as people "De-smoged" and cleaned up under their hoods!
