Adjustable Vacuum Advance

Post #17. MVA is not dealing with the top of the advance curve [ higher rpm ]. It deals with lower rpm.
Larew wrote his book in 1967. Obert I believe is even earlier. As I stated in post #15, & gave an example, many things have changed over the years as more knowledge & research have shown that some original ideas were wrong....
Chrys used MVA in the 1970s.
From my 1972-78 MM, p. 2-457. 'When coolant temp at idle reaches 225*F, the valve opens and applies MANIFOLD VACUUM directly to the dist....This increases engine idle speed & provides additional engine cooling.'
The engine could care less what the A/F is at idle, it is trying to cool down.
It should be veeery obvious what is happening here: with the extra timing at idle, the engine is making more hp, which is reflected in the increased idle rpm, since at idle the engine is powering itself, & not moving the vehicle.