I have a small tuning issue that I am trying to decide how to fix.

I have my cruising A/F range between 14.5 and 15.5 below 65mph or so. When I am cruising and I let off of the pedal, the A/F drops down into the mid 13's. I am assuming that the vacuum goes up which pulls more fuel making it rich. How do I correct this?

I am currently running a distributor with out a vacuum advance canister. If I had a vacuum advance distributor, would this correct this issue?

Thanks