Timing issue
 

I am fighting a bizarre problem with my distributor in my 302. For some reason it wants to have all the timing in way too early. Right now with one heavy and one medium spring it is all in at 1700 RPM. I took the distributor out and thoroughly went over it and did not find anything strange. Earlier I had both heavy Springs in and they were all in at 2100. Has anyone ever ran into this before. It is the stock Z28 distributor

make sure the limiter bushing is in place. if it is missing it can cause this problem.

It's still in there. I did use some jb weld to limit the advance on one side of the slot. Maybe I did the wrong side? As you look at the picture I did the right side of the slot. So if you pull the weights out the bushing goes back and pushes against this right side

are the weights held against the 'at rest' position by the springs?- requires effort to move the point cam off the at rest position all the way through to the full advance position? any slop in the at rest position? maybe weights are modified or not compatible to the distributor shaft top cam?
you are checking timing with vacuum advance disconnected? no slop in vac vac?
at idle is initial timing reading stable?

The distributor had been set up and restored and then checked over by another shop before I put it in the car. I put the weights and springs on a spare distributor a friend of mine had and it was right on. So the only thing I can think of is something with me putting the J-B Weld in the advance slot really screwed it up.

Springs determine how quickly the advance comes in, the slot length determines total amount of mechanical advance.

Do you have the stock weights? The original springs are so strong, that you need a screw drivers to release them.