My '64 has an older 390 that a PO swapped in. It started running a little rough a couple months ago. Main thing I had to do was adjust the idle up.
Now it's running rough and missing. It will seam to idle well and when you operate the accelerator the rpms go up but then drop off. I suspected the carb first but it is getting fuel. I was checking the timing and points and it seamed like the plate that the points are on moves too easily. When I hooked up a dwell meter it would read in the neighborhood of 36* but as you rev up the engine it would shift down to almost 24*. This with the vac adv disconnected and plugged. I tried to set the point gap to the manual but this didn't really change anything. Your thoughts would be appreciated.
Thanks.
John

 

Rotate the engine to where the points are completely closed. Then, push and pull on the distributor shaft inline with the location of where the points contact the distributor shaft cam (if that makes any sense). If the points open and close as you do this, the upper bushing in the distributor is shot, and the dwell is walking all over the place.

When I first got my '74 highboy from my brother when I was 19, within a few months, I was chasing just about the same type of demons you are. The distributor bushing was my problem.

Of course, your problem might be something else, but we'll work through it

 

Thanks for the idea. I'll check that in the next couple days. I have noticed that the upper plate that pivots when the vac advance operates, has some play when pushed on, in the front to rear direction. It does affect the points when it does. I have a petronix unit on order.

 

I've seen the breaker plate wear out. Your saying it's loose so I'd investigate. Once it gets play in it, it wont run right no matter what you try.

 

I pulled the distributor this weekend, Unfortunately, the breaker plate is held to the other one with a one way retainer nut that is pushed onto the stud. Most videos i watched, this was an e-clip. This is where I think there maybe a problem.Bushings seam good. This weekend, I'm going to try the petronix to see what happens.
john