Vacuum Advance?
 

Engine won't idle down after letting off the gas. If I give it a quick kick it will usually drop down. Last time out it was bogging and jerking when cruising when hitting the gas. I think the vacuum advance is sticking. Haven't pulled it apart yet but wondering what's good to clean it up and get it working. It's a GM HEI distributor.

Probably just needs the advance weights and pins lubed up.
Make sure the springs are not broken etc.
If it is a GM dist it may have white nylon pin bushings
They are available from NAPA.
GM hei distributors suffer from spark ionization....that brown dust.
Drilling two 1/4 in holes in the back side of the cap cures that.
Vac advance should be conected to full time manifold vac port.

Well thank you for waking my brain up. I haven't had a chance to look at it yet but if I had I'm sure it would have dawned on me. The vacuum advance activates the mechanical, they're not independent. Been awhile since I had to work on one.

Hmmmmm the mind is the second thing to go !!

What mind?

Well I pulled the distributor apart today. Looked good, both mechanical and vacuum advance seemed to be working smoothly. Cleaned it up a little and put it back together. Still runs like a pig. Too hot and humid and too late to throw a timing light on it, maybe tomorrow. Only other thing I can think is vacuum secondary's. If they're partly open that would keep the idle up, if they kick in too soon that would cause a bog. Maybe something else to tear apart. It's always something.

Had the exact same issue. Replaced the accelerator pump... did the trick