slowgoer,
I might be as 'retarded' as you. I will give my version and let the experts set us both straight.
If you can draw a vacuum, with your mouth or a pump on the vacuum advance unit, and it will remain retracted until you release the port, the unit is good. You did this and proved yours to be fine.
Engine vacuum is highest at idle. At idle, your unit should have pulled the distributor counterclockwise and held it there.
If the distributors normal rotation is clockwise, then a vacuum retracted unit will hold the distributor in a advanced state until vacuum drops, and the internal spring shoves the distributor back towards it static position.
When you loose vacuum, it usually means an increase in engine RPM, which will bring the centrifugal advance into play.
The system will never go into a 'retarded' setting. I think you have only initial advance, which you set with a light, then you have vacuum and mechanical advance. You can never get past initial advance, so in theory, cannot get to a retarded state.
Your vacuum advance unit has to move the distributor pretty easily. You should see it do this. If you are using the port on the carburetor intended for this function, as soon as you crack the throttle, that distributor should move.
The mechanism must not be bound. The internal spring inside the vacuum advance unit is quite stout, but things must be free.
Some types of distributors only move the plate inside the distributor housing, but I don't think any of the old GM's were like this.
I might have to eat some humble pie, as this may not be the way it actually works.
Stuart
