Still having timing trouble 401 AMC

I think I may have asked this question before but here goes again. When I try to set my timing, the mark varies up and down aprox 5 deg and will not stay in one spot. I dont know what is causing this problem. A vaccume test shows late ignition timing and now when I turn the dizzy in either direction the engine will stumble resulting in a low rough idle, so there is no increase in smotheness either way. I pulled the Dizzy and can find no slop in the bushings other than when I turn the shaft by hand the centrifiguel weights begin to spread before the points open. dead horse

 

Worn out timing chain?

 

That would make sense. Will a timing chain cause low manifold vacuum?

 

Not necessarily. Vacuum bounce around? You do a compression check?

 

Earlier on, but the guage I was using was not in the greatest shape. The camshaft was another suggestion that was given. I dont want to overlook any obvious problems ie vacuum leak, carb, ignition wires, etc before pulling the darn thing apart. The PO claimed that the engine was pritty fresh. I guess he ment degreased and spray painted?

 

You have a vacuum gauge?

I would also try and eliminate that the jumoing around is coming from misfiring due to whatever - leaky valves, bad cam, etc. I other words, the engine may have a problem that makes the timing mark jump around, rather than the engine runs badly becasue it's out of time.

 

Yes I have a vacuum guage and the reading I got suggest late timing. The guage shows steady low vacuum at aprox 16 lbs. The niedle does not jump at all. When I snap the throttle the guage responds accordingly. When I attempt to adjust the timing, engine vacuum remains at 15 to 16 lbs. I get the same results when adjusting the air fuel mixture, no signifigant change in vacuum.
The issue is these adjustments used to make a signifigant change in the engine idle, now makes little difference at all, so what ever the problem is, its steadely getting worse.