Vacuum advance information and myths

A lot of BS creeping in here. Post #58 claiming the switch to PVA had nothing to do with emissions is BS. It had everything to do with emissions. GM, who used MVA, could not meet the stricter HC emissions standards coming into effect in the late 60s & had to switch to PVA. Switching to PVA retarded idle timing.
From the Holley book: ' the retarded spark helps to reduce HC emissions by raising exh temps....'...&....'The use of retarded spark requires richer jetting in the idle & main systems to get off idle performance & drivability'....& ...'Because retarding the spark hurts efficiency, the throttle plates must be opened further at idle to get enough mixture in for the engine to continue running.'