I am currently running a mechanical advance distributor and my 30mph to 75mph cruising A/F shows 14.2-14.6. If I was to swap from a mechanical only distributor to a vacuum advance distributor, and I kept the initial and the mechanical the same, what would my cruising A/F do once the vacuum advance is added to the curve? I am assuming that I will I see the whole curve go leaner, would this be correct?

My A/F currently goes richer once I am at a cruise and I let off of the accel pedal. Would the VA distributor keep the A/F leaner since there is more vacuum made during decel?

Thanks

I would expect it to read a little more lean on decel when under vacuum with the extra spark to burn the fuel. During a stead cruise under normal load, I wouldn't expect to see a big difference in a/f, maybe a couple .points.

I was hoping only a little bit.
Thanks for the reply.

the increase in advance will lean up the fuel curve.

Short answer: Basically No. But it does change the products of combustion. Fuel & air at any given rpm and throttle position should equal the total combustion products and air out. But the WBO2 doesn't measure them all. So it may indicate a change in AFR when there is none.
A more complete answer can be found by searching Innovate's Forum. Here's one that is pretty thorough Is it ready for the track, post numbers 10 & 16.

Mattax,
Thanks for the PM and for the link. It was good reading.