Timing by Vacuum Reading?

Duster Bob,
Let me apologise for post #6. I came across a bit 'too' heavy & I don't know the bold print got in, only meant to 'bold' a few words.
I have been doing this for 40+ years. Back in the 70s, I was mounting solenoids on the sides of dizzys because I couldn't get adj vac adv units HERE to increase idle timing. The sol pulled in the breaker plate to advance the timing once the engine was running. Not a perfect set up, but better than nothing.

Ign timing is a most MISUNDERSTOOD subject, even amongst seasoned mechanics.

No apologies for what I am about to say because some of the comments above are just NONSENSE without knowing the cam specs. Such as initial timing is within 10-16*. You determine initial timing from the procedure in post 6, & that is where you start. Many racers used to & still do, 'lock' their dists. That means if the engine made best HP with 40* of timing, the engine also idled with 40*. My engine has a locked dist, 35*. My adj vac adv unit, which is connected to manifold vacuum, adds 13*. So it idles with 48*. [ Ported vac adv is useless. MVA does everything that PVA does, & more ]
David Vizard. Author of 30+auto books & over 4000 articles. Consultant to F1 teams, major auto companies, cam companies, you name it.

This is what he says about idle timing in his Holley book [ think about why idle timing might be important for setting up a carb ].
"The optimum idle advance is typically about 35-40* for a short cammed street engine & though not commonly realized ] ** ain't that the truth** as much as 50* for a street strip engine".
Elsewhere in the book: 'To get an optimum idle....timing often needs to as much s 45-50*'.
It gets mentioned in a carb book because idle timing is the starting point for tuning the carb's idle circuit. NOT the other way round.
By using an adj vac unit, which works down to about 6-7" of vac, you add the extra timing reqd for best idle quality, highest vac & best off-idle tip in response. The engine makes more HP at idle when it has the correct idle timing, so that it carries the load off idle without a stumble.

More specific to Mother, p. 34 of Mopar Muscle magazine Oct 2015. "Initial timing went from 15 to 26* while adding an inch of vacuum......a dramatic gain in low rpm throttle response was realized. "