rough idle - alternator?

[JackFish]

It's rough and missing at idle, cold or hot, less so when cold. OK at cruise.
No valve train chatter to speak of.
I've:
Swapped the coil, plugs, wires, and cap.
Took the carb off and cleaned it thoroughly. It was missing the check ball and weight, but their addition has not solved the problem. And set the float.
Isolated EGR vacuum, it's steady, and the manifold vacuum seems to function OK. It was steady around 6-7, dropped to 0 opening the throttle and up to 15 at high rpm, then dropping back down.
Compression came in @ 166, 170, 174, 174, 164 ,160.
Swapped the PCV valve.
I ordered a new three port PVS and have to check the vacuum on that some more, but I am wondering if the problem could be the old alternator and if it could cause the rough idle before I pull it and take it in to be checked.

There is also a crack in the exhaust manifold close to the choke port.

 

[66 Fastback]

The manifold vacuum seems low.
What kind of rpm's are you idling at in drive?
Vacuum leak?
Vacuum leak on one of the vacuum motor such as the vacuum advance on the distributor?
Ignition timing off?
Slipped harmonic balancer/timing mark leading you to believe the timing is set to spec when it really isn't?
I doubt it would be the alternator. As long as the battery is fully charged, it should run OK even if the alternator is weak.
Doug

 

[JackFish]

Ya, I have been thinking vacuum leak as well.
Will do a bit more testing a write down some specific numbers.
What do you think manifold vacuum should be? It is an automatic, with power brakes, AC.
Haven't checked the timing. Will get the light out, but with it running so rough it will be approximate anyway.

 

[Bort62]

Manifold vacuum at idle on a stock motor should be about 20".

Where are you measuring it?

 

[JackFish]

I pulled a line that goes from the intake manifold to the air cleaner bi-metal sensor.
I'm looking at the Chiltons at the moment and it says vacuum should be above 8 inches, so even at that I'm low it would appear.

 

[JackFish]

Fixed. Busted PVS.
And a compression guage that was off by about 7psi.