I thought I'd start a new thread here since my original thread about the no start issue has taken some twists and turns.
Recap: car is a 1974 2.0 which I have changed the plugs, plug wires, dist cap, rotor, installed a pertronix unit, adjusted the valves and set the timing.

Problem now is the car stumbles, and idles erratically revving up, then down, almost stalling, then back up as if to catch itself. This is with the vacuum line attached to the retard side of the canister. The only way it smooths out with vacuum attached is to set the idle at about 1200 rpm. With vacuum disconnected from dizzy, will run smoothly at 950 rpm.

I don't think there are vacuum leaks because it seems as those would cause a high idle, not this stumbling problem.
It's like when the timing is retarded by the vacuum, it runs like shit!
Ideas?

Thanks,
Bill

What is the condition of your distributor inside? The points plates lubed and moving well? If it's all gunked up, it can cause issues. How about the charging system?
All the electricals in good shape?
It's possible you've already looked at this webpage but it's got a lot of procedures
and troubleshooting for components : http://members.rennlist.com/pbanders/idle.htm
I always mention this but a good Air/Fuel gauge will give a great picture into what
you mixture is doing and makes it easier to troubleshoot weird issues like this.

Hey, thanks! Great link there.

Charging system good. Electrics good.
I will check the points plates. The other thing I'll do is check the TPS.

What happens when you run without the vacuum retard hooked up? Just curious.

Definitely check your TPS adjustment. Is your AAR hooked up and working?
If your retard is not hooked up, I'd think it would be like a vacuum leak and cause
high idle. Do you have the hose completely unhooked and not plugged?
Idle hunting like that can be a lean fuel situation but I'm confused about it running
better with the retard unhooked.
The Brad Anders link is a wealth of D Jet resources and is what most of us use as
a reference. Be methodical in going through all the components and make note of
any components that are mismatched for your model year...it can make a difference
in how things work together. Also try unplugging the Temp sensor on the plenum and see if it makes a difference in how your idle sounds with the retard hooked up. It's
the sensor close to the TPS by the throttle body.
Hopefully, over the course of the weekend, more people will offer suggestions to you
that I might not have thought of!

Well, I've adjusted the TPS and checked the plates in the dizzy. They will move if I move them by hand, but not if I suck on either port with a vacuum hose. Canister bad?
The thing is, with vacuum attached to retard, it does something because it affects the idle.
I drove the car today with retard unhooked and it runs fine. If it's just there for emissions at idle, there is no harm to run it with out it, correct?
Why not just plug off the ports on the canister and the TB and not worry?

The vacuum is there for a reason. Pull the hose to it and suck on it while watching if that moves the advance plates while the cap is off

I did that. Plates did not move when sucking on hose. They will move by hand.

Canister?

In that test do you detect the ability to build and hold vacuum? You may need a new canister/pot

Will not hold vacuum. Can I replace the pot with the dizzy in place?

Maybe? Easier to pull the dizzy and retime

Basically, no. Nearly impossible to get at one of the screws. Good luck finding the correct replacement. However, IF you connect the retard hose, and it retards the timing (pretty obvious, the idle drops), then your testing is faulty.

The Cap'n

That's what I was wondering. Not really holding vacuum when suck on hose, but hooking it up does affect idle. I've used a vacuum hose that fits the port well and does not leak.
Anyway, any harm in not having it attached at all?

There is an issue with the screw used on some optical sensors that protrudes enough to bind up the advance plates.

Easy fix, grind down the screw.

I would suggest you see , by hand, if everything moves as it should inside the distributor....

That would be best done by removing the distributor, but if you don't want to do that, remove the c-clip that hold the vacuum canister arm to the advance plates and after the arm is removed, fell how they move.

When they are dirty with old nasty grease from 40 years ago, they get really tight when hot and won't move back to normal idle unless forced.

The retard vacuum might have enough power to do that sometimes, but not all the time...

Rich

If you run with it off, you're gonna have an high idle, which may be correctable by turning in the air bleed screw on the throttle body, but then you begin a long chain of compensatory adjustments. The first of those will be the loss of the instant 5-10 degree advance when the throttle begins to open. That probably means a flat spot, maybe almost nothing, or maybe something pretty significant. Might have to adjust the idle mixture, too, and then reset the idle screw. It goes on from there, chasing the elusive good idle and good drivability off idle.

The Cap'n

Okay, I've removed the vacuum canister. Holds vacuum on the advance port, but not on the retard port. I assume the diaphragm is torn. Need to find a working unit. O'reilly's has them for a 1973, but not a 1974. Not sure of the difference. Would rather have a Bosch or Porsche unit anyway.
Any idea where to got one for a 1974 2.0?

Those are hard to find and if you do find one, it may not hold vacuum either.
I managed to get a good dizzy with a working canister from Bruce Stone last year.
He's a member here and is a good parts source "bdstone914" is his handle here.
Or just place a WTB ad in the classifieds here.

Just an update here. I put another vacuum pot on from another 1974 2.0. It has solved the problem! Purring like a German kitten should at the proper idle. Ya'll were right about the response on takeoff as well.
Thanks!!