It's an idle problem. The idle speed drops drastically when I put the car in gear. It even drops if I turn on the electric fan. Any load on the engine drops it.

I changed the carb shortly before I changed the distributor. It's a Street Avenger 670. Runs like a dream above idle. I just don't remember if I had an idle problem with the new carb before I changed the distributor.

I ran the HEI with timing set at 18 degrees initial and 34 total.

The early-style distributor doesn't have a bushing to limit the mechanical advance, so I have to run with 8 initial to keep 34 total. Of course, this means that I'm depending on the vacuum advance to give me the necessary advance for a decent idle.

Is the vacuum advance dropping out when I put a load on the engine? Or is the carb the culprit?

A combination of the two?

It's hard to tell. I definitely prefer more initial timing. I think I'm gonna drop the HEI back in there since it's all set up for the MSD trigger now.

this exactly my pet peeve with using vacuum advance at idle. You put the car in gear, the idle drops, the vacuum drops, the timing retards, the vacuum drops more, it's vicious circle type thing. I almost never run vacuum advance at idle just for this reason. Is there a ported vacuum port on that carb? If there is hook the dist to it and bump the initial as far as you can. you may need to limit the travel of the vacuum advance to keep from adding too much at cruise and getting into a pinging situation.

Let us know what happens here.

Tom

The more I think back, the more I remember the carb working fine before I changed the distributor. I was worried that I'd bought a faulty Holley.

One other symptom is that it holds a very fast dle under deceleration (almost feels like the throttle is stuck), until it reaches the point where the trans and converter release the engine. At that point it drops. More evidence of the vacuum advance holding the idle speed up and dropping it under load.

You're right about the "vicious circle". That's exactly what it seems like. I have to brake with the left foot so I can keep the car running with the right. Not fun.

I can't find limit bushings anywhere other than mail order, and they come with only one in the kit.

Try some heavier vacuum advance springs and see what happens. Make sure that the weights are lubed as well.

If you pop the hood on a early to mid eighties AMC eagle and many others from these years, you'll find and assortment of vacume limiting inline doohickeys? :D I keep an assortment of these for tuning the vacume signal. You'll notice they are color coded. They look like a very small inline carb filter. Get yourself an assortment and use a mityvac hand held vacume pump to record what they do. Some delay the loss in vacume like a slow closing one way valve, others only open at a set vacume. These can help tailor the vacume signal to your advance. I have no idea what they are actually called but they are related to all the vacume operated emissions used back then.
Better yet, fix the mechanical advance curve and plug the vacume advance in on the ported nipple. Or don't use vacume at all but the fuel mileage at cruize speed will drop.

This morning I put it on ported vacuum and had to open the throttle plates too much in order to get it to run at idle speed. I got run-on when I killed it.

Keith, I already had the heaviest springs I could find on the mechanical advance.

If I had the limiting bushing, I could have solved the problem, but it didn't work out that way.

The full report is here: Distributor Experiment, Phase 1 (http://www.chevelles.com/forum/ultimatebb.php?ubb=get_topic;f=4;t=018902).