my experience with it, is that it made no discernible difference one way or the other whether the vacuum advance is operating or not. I drove around for I don't know how long with it disconnected completely. (not on purpose) As a matter of fact this is the first time I have heard of it affecting anything. But tis wonderful you figured it out. (the "tis" part is because christmas is coming) But then again, I'm not presently running any heat to the manifold. And haven't been for a year now, and it runs great.
