vacuum advance issue? (331 poly)

Can anyone please explain the function of the the vacuum advance? We have gone through this engine several times by several people & can't find a continues mis. If the advance is disconnected it will run, roughly, but it will run. Connect the vacuum advance & it barely runs. I should note that this engine is a modification, it has dual quads ala the full hemi. Could this be part of the issue?

Thanks

Torry

The vacuum advance is mainly for fuel economy. It advances the spark under high vacuum conditions (cruising, throttle nearly close) and backs off under low vacuum (wide open throttle).

It won't work as well with dual quads because engine vacuum will be lower. But Chrysler offered dual quads in the fifties, you should look up the specs and compare them to the single carb engines.

I don't know what the problem is but I don't think the vacuum advance is causing it. Disconnecting the vacuum advance will retard the spark a little. If the vacuum advance diaphragm is ruptured it will cause a vacuum leak and plugging the line will stop the leak. Other than that it shouldn't have much effect.