This morning, I discovered an article helping to diagnose distributor problems.
> Distributor wear diagnostics <. I hooked up the timing light to the coil wire (per the article) and watched the timing mark on the pulley. As I witnessed yesterday, the mark jumps around moving about an inch more in advance every few sparks. The article says the explanation for this is bearing wear causing the shaft to shift and point gap change.
I had difficulty starting the car and quickly learned that if I choked it at all, the engine stalled. (suggesting my 20 flats open was way too rich with the engine cold) I set the idle higher and without adjusting the carbs, started the engine and was able to get it to run for two minutes at 1200 rpm. Suddenly the engine stopped as if I cut off the ignition or fuel. After waiting 10 seconds I started it again and it continued to warm up.
I checked the timing light again and saw the timing mark jump back and forth as it had previously done. Because the article said this is a worn distributor, I decided to put the Portronics distributor back on. This is a new distributor which matches the old, but has a magnetic pickup inside to eliminate the points and condenser. I was sure this would eliminate the "wear" problem I initially witnessed.
I started the engine again which was still warm. I rotated the distributor to get the smoothest idle I could and was able to reduce the rpm to 700. (I didn't try to reduce it further) At that point, I looked at the advance again and saw the timing mark move as it had done with the old distributor. I took a video of the event, but the file size is too large to post (29meg) and I don't know how to compress the file.
I'm wondering if it could be caused by too much end play in the short shaft that drives the oil pump, tach, and distributor? It's a helical gear which could move axially if there were too much end play. This would affect timing, but I find it hard to believe it would jump back and fourth. Does anybody have experience with this? Or do you have another explanation for the timing to jump with a new distributor?