[Gaz64]

Rune,

Any further with your problem?

A dual diaphragm advance can may allow you to retard the timing as the engine is decelerating towards idle, almost "forcing" the engine to idle.

As the engine is say 20-50 rpm above the normal idle speed manifold vacuum would have dropped off enough, and the advance could then be coming back at the same time.

Hope this makes sense.

I have done this with a MSD 6AL-2 6530.