Originally posted by 76GMC1500
I have to teach myself everything I know about cars, but it seems that vacuum advance would retard the timing under acceleration. When you floor it, the engine is still not spinning very quickly, so it would have a tendancy to detonate. Also, manifold vac drops significantly, so if the ignition is advanced as vacuum increases, then it would retard as vac decreases.
Well... yeah it would "in theroy" retard when vacuum is decreased but actually it would just return to zero vacuum advance and use the initial 'set' advance. The thing is, in order for it to actually 'retard' the timing you must have a diaphram setup to allow that. Ford does have dual diaphram vaccum advance units that allows this. Mine is not. You can either set it to be at full advance (mech/vac) at idle by manifold vac., or set it for no advance untill throttled (mech advance until throttle plates are opened) known as ported vacuum.

Also, that is why carbs have an accel pump - to keep the engine fed with fuel until it regains enough vac to draw from jets. So, not having the vac advance hooked up shouldn't make the engine fall on its face unless it were to advance so quickly that engine began detonating badly. And finally, vac advance is like a precurser to electronically controlled ignition and knock sensors. If your spark is advanced enough to give you any kind of bad knock, manifold vac would drop, retarding the timing.
Yeah that sounds about right. I'd explain it a little differntly but I think you have it there.

Plz tell me if any of my thinking is wrong.