To my surprise
,I found that the vaccum advance plate had not been moving, because the screws holding the pickup were too long! When tightened down, they press down on the vacuum advance plate (below), locking it tight. From what I can see, to work correctly, they must be only long enough to catch the threads in the upper plate (directly below the pickup). If they protrude through those threads, they are too long. Now, what has me puzzled is that I replaced that pickup first thing after I got the car, because the wires were frayed and shorting. I don't recall the old pickup being any thicker, but I tossed it, so I can't compare now. Has anyone run into this before?
I'm guessing that the screws were replaced by some mechanic
who did not realize they were too long. In any case, the vacuum unit (which actually moves nicely under vacuum) has been struggling to move the plate, and the strain (or perhaps old age) has snapped the small plastic connector (that attaches to the threads on the vacuum advance unit and slips onto the round peg attached to the moveable plate).I have temporarily (until I locate a replacement) epoxied the plastic connector back together, and inserted "spacer" nuts on the topside on the bolts holding down the pickup.
So it is clean and back together (with a new paper gasket). The entire distributor seems to otherwise be in good condition, and the vaccum advance is now moving correctly under vaccum. If anyone has had this experience and has advice, I'd appreciate it. I wish I'd kept the old pickup, but I remember it looked identical at the time.
I'm just wondering if I've done something really stupid
and can't see it.
crazy.