So, it turns out I was wrong--but this time I really have figured it out. I think. haha.

I went through and reseated the secondary throttle plates. I could not eliminate all light around the edges when they were seated in the bores, but I got it the best I possibly could. Upon installation, it seemed there was an improvement at first, but once the engine was really good and hot (as in, after a road test), it was clear nothing had changed.

Usually I have had the air cleaner off while running tests on the engine trying to solve this issue. Today, I happened to listen to it from the passenger side with the air cleaner on, and from that position I heard what sounded like a major vacuum leak. Eventually I found the source: the choke thermostat. When the choke spring got hot enough, the little piston inside the choke mechanism dropped far enough in its bore that the vacuum supply was allowed to completely bypass the piston. It was at this point that my idling problems showed up.

The cause? The new base gasket that came with the rebuild kit. The bore holes are much too large. Instead of passing through a restriction in the carb body, manifold vacuum was passing directly to the choke hole. Once the choke piston was far enough down its bore to be bypassed, the choke heater became a vacuum leak. The reason I was able to tune the engine so well previously was that at the time I was using a gasket I made from some material I had handy, which was quite well-matched to the actual throttle bores.

I removed the choke stove pipe and blocked the heated air intake. There was immediate improvement. So, now I just need to find (or make) the right gasket!

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

Thanks Ted! I have figured it out, though I haven't fixed it yet.

It's the AFB secondaries. Even when I hold them closed as snugly as I can, they are leaking air, and since they have no idle circuit it's the same as a vacuum leak. I should have checked them more thoroughly before. Back when I had the mixture at 1-1/8 turns and smooth slow idle, the secondaries were sealed shut with old fuel varnish. That varnish has since been cleaned off and I made sure the secondaries were not stuck--at the expense of idle quality apparently.

It's looking like I will have to loosen the throttle plate mounting screws and re-seat the plates in the secondary bores.

I'd heard these vacuum secondary AFBs were troublesome, so I suppose I shouldn't be surprised!

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

I’ll suggest hooking up a battery charger to the battery while the engine is idling and see if the idle quality improves by doing so. If the idle at low rpm does indeed improve by doing this, this gives you an idea of what direction to take in solving your problem.

Lorena, Texas (South of Waco)

I got the new regulator on. As far as I can tell, it performs exactly the same as the old one. At least now I'm sure, and I have the old one as a less cosmetically appealing spare

Still having idle problems. The beautifully smooth idle down to 375 RPM is gone. Now the smoothest I can get it is at about 650 rpm with the mixture screws out 2 turns. Tried playing with all the usual tuning parameters (mixture, idle speed, timing) and unable to improve on that. Checked the distributor shaft but it feels like it's still moving freely and returning to rest. Checked to make sure secondaries weren't floating open but holding them closed by hand made no difference. No trouble idling in gear, it's just sloppy. Don't know where my consistency went, but I suspect more ignition problems, or possibly the valve adjustment needing to be revisited yet again. Runs awesome off idle though.

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

I would do that. In the old days on the farm we always had a few extra voltage regulators hanging on the wall because we didn't trust them. In fact I have one out of a 1977 F350 hanging on the wall right now.

Mark

1956 Mercury M100
1955 Ford Fairlane Club Sedan
Delta, British Columbia

Maybe the problem indeed is not completely resolved.



I have continued to get reliably from point A to point B as I've driven the car since last posting, but on one occasion with the lights and blower on idling at a traffic light there was a flicker of the old trouble, and twice when coasting to a stop in front of my house the engine has stopped altogether.



Pete, are you certain you're correct about the car's power coming from the battery? My understanding and observation has always been that the battery's purpose is only to start the car and store energy for when the charging system can't keep up, and that a running vehicle will continue to run with the battery disconnected. The charging system restores the battery and supplies power for the running vehicle. Either way, a faulty battery would not keep starting the car, especially in dropping temperatures, so I think my batt is ok.



I have ordered a replacement 30A voltage regulator to see how that affects things as I have already expressed some doubts about the function of the current unit. I'll post back with any updates.

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

I'm still not 100% confident in my voltage regulator's performance, but I believe the battery is sound. I have started the car too many times to count and have never had to jump it. I've started actually putting some miles on it over the past week and it continues to run well and reliably, so I think I can give the battery a clean bill of health for the time being

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

I bought my wagon in Bend Oregon and drove it home to near Denver Colorado. In western Wyoming the generator failed. With the help and advice of this forum, I drove the final leg of my trip with no generator, only battery. Made the trip fine and I think I could have gone quite a distance further. A good battery will get you quite a ways.

Jim - Erie Colorado, 1957 Country Sedan

Thats a good suggestion.A load test will tell you real quick if the battery is no good.

  

peeot

I am glad to hear that you have the car running well again. But I do not think you have found the real cause of the problem. A cars electrical power ALL comes from the cars battery NOT from the generator or alternator. The gen and alt supply power to the battery and then the battery supplys power to the ignition and lights and all the rest of the cars electrical needs.

If you had a fully charged up battery and removed the fan belt that turns the generator your car will start and run until the battery is discharged. The fact that your car ran until the voltage to the coil dropped to 8.5 volts  make me wonder if you do not have a defective battery. It might be worth checking. Pete

I