Mr. Hanlon, if disconnecting the vacuum advance causes your ignition timing to retard at idle, then your vacuum advance is mistakenly connected to MANIFOLD vacuum. It should be connected to PORTED vacuum instead. PORTED vacuum is found on one of the vacuum ports on your carburetor. It should supply vacuum to the distributor's vacuum advance only when the throttle is open. The more throttle, the more PORTED vacuum, and the more the ignition timing is advanced. The only time vacuum should be routed to the distributor at idle is if your car has a ported vacuum switch--a device designed to send MANIFOLD vacuum to the distributor as the engine is warming up. When the engine reaches operating temperature, then PORTED vacuum is restored to the distributor's vacuum advance. This was a commonly used device in the 70's and 80's.