As mentioned it could be a combination of problems compounding. I would at this point start swapping parts out with known good ones if possible (carb, distributor) and if that did not fix it then start to look at other things but at least you will have eliminated then as the problem.

Greenbird, thanks for your thorough and informative post. I have always intended to test and tune the advance curve. I have been waiting to sort this issue out to try it. I have assumed that the curve is not critical to hot idle issues because it is a static value (initial only) at that engine speed. I have checked and confirmed that it is indeed static at low RPM many times. A cursory study with vacuum advance disconnected shows that advance begins around 700 crank RPM and hits the second spring probably around 1800 rpm and 10* of additional advance. It looked like it maxed out around 20* of advance on top of the initial. Perhaps not optimised, but nothing highly irregular.

I was away on vacation for a week and am back to take another look at things. I decided to ignore the idle/miss/die in gear and take care of the stumble I have mentioned. I have always thought it was the accelerator pump. At first, I had an old pump in there. Then, the new one was binding in the bore. I examined the bore more closely and it had some "texture" so I attempted to polish it with my dremel tool until the new pump was moving smoothly. I put a little oil on it and installed; it wasn't binding at first but as soon as it had soaked in the gas long enough it was binding again. I removed it and put the old one back in, and ever since I have had a nice consistent pair of streams of fuel from the pump. It appears, to my eye, to be as sensitive as it ought and delivering an acceptable volume. The stumbling, however, remains. I tried all three pump rod positions, no change. I tried choking the engine manually AND maximum pump volume and still no change. To open the throttle suddenly FROM IDLE SPEED is to stall the engine. I tried completely disconnecting the pump and there was still no change in behavior.

I noticed that the main boosters are beginning to discharge at about 1500 rpm, when there is still at least 1/4 of the idle transfer slot exposed above the throttle plate. Even with the accel pump disconnected, before the engine stalls when I snap the throttle there is some discharge from the boosters. Combined with the fact that my mixture screws prefer to barely be open, I concluded that I was probably dealing with a RICH bog and not a lean one, so the float setting, though set to spec, must be too high. I lowered it 1/32" and repeated the tests with no change to ANY aspect of performance.

By the end of all of this the engine had reached that stage in its troubles where it became difficult to start. I set up my good timing light and saw a perfect spark signal as the engine spun over but wouldn't start. To start the engine, I had to treat it like it was flooded, even though there was not any fuel leaking in (above the throttle plates, at least).

After lunch, I intend to go out and continue to lower the float incrementally until I notice some kind of change. Will post back then.

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

I dropped the float as low as 5/16", double the specification. I didn't notice any difference until I dropped it that low. It became very difficult to start. When I got it started, the boosters did not flow at 1500 rpm, but had started flowing by 1800 rpm. I had to open the mixture screws up to 1.5 turns to get it to start, but once it started, it wanted them back at the usual spot of about 0.5 turns. Other than these things, every other aspect of performance was unchanged. Smooth, steady, miss-free running on the lowest step of the fast idle cam; missing and soon stalling at hot idle. Timing set to about 11* initial. Misses on the vacuum gauge involve a drop of about 0.5" Hg each. Timing light shows spark present always. Sudden throttle motion causes a stall. Blah blah blah.

At least it's consistent.

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

I marked a piece of tape with timing marks at 5* intervals up to 50* BTDC. With the engine thoroughly hot, it would go into gear without stalling immediately ONLY IF the timing was 27* or more. With that much advance, the stumbling problem also vanished.

Why could it possibly require so much advance?

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

Old question - you're sure of the TDC location you are basing this on? Just checking....... 27º seems like a lot to me too.

The Y-block stocker cylinder heads typically need some early low rpm advance to work well. I use 17º (10º initial plus 7º of live manifold vacuum advance) to get the best idle vacuum on my outfit. Stock "C" heads, factory cam and tuned for this arrangement. Several have told me they use 14º initial and ported vacuum to the distributor. Anyway, half of the 27º and a little bit more wouldn't be unusual.

 
 Steve Metzger       Tucson, Arizona

I,m with steve, obviousley that much initial advance is not usual amount and we know how thorough you are, I think the TDC mark may need rechecking then see if the distributer is not a tooth out, but glad to see some of our initial suggestions re advance settings have made some improvement as we were all starting to doubt our own knowledge. looking forward to your findings. regards bill.

  AussieBill            YYYY    Forever Y Block     YYYY

 Down Under, Australia

Have you considered setting the timing using a vacuum gauge like the oldtime machanics did?It would be interesting to see where the timing ends up if you did it using a vacuum gauge as compared to where it is with the timing light showing 27 adavance.

  

Indeed, I have checked TDC and the crank marks more than once and am confident that they are accurate within 2-4 degrees. I remember checking for it when I had the heads off too, when it's easiest to see.

I watched the timing and revved the engine up a bit before attempting a test drive. According to the marks, I was hitting the mid- to upper-thirties on the 1st spring alone, then continuing to accelerate the engine pushed the timing into the forties. The engine didn't seem to mind it, so I left the vacuum advance disconnected and took a spin. It was very nice to have a responsive throttle again. I could mash the throttle at any time and get a rush of power. If I pushed it hard enough, I did at times detect some spark knock, so needless to say I wasn't too rough with it. I did some stop-and-go and also some highway cruising at 3k rpm, everything felt fine and the engine was definitely running closer to the middle of the temp gauge (that is to say, running cooler) than it had last time I took it on the highway. I picked a route that avoided stops and two-footed it when I had to sit. When I got back to the driveway, I took my foot off the gas and the engine died pretty much immediately. It then started right back up in neutral, but stalled as soon as I put it in gear.

So, whatever it is that's going on, there comes a point when even all of that extra timing doesn't help. I tried advancing farther, retarding, enriching, leaning, idling up, idling down in too many combinations to mention through the course of today's tinkering but ultimately it was clear that no matter what I did it would not start behaving like a proper engine.

Wanted to mention that I temp-probed both the Chrysler and the Ford in several key places (exhaust crossover under carb, carb itself near mixture screws, exhaust manifolds, exhaust pipe before and after muffler). I wanted to be sure it was worth my while to remove the mufflers to see whether they were over-restricting the exhaust, which I have thought to be unlikely. Both engines showed very similar temperatures. Most important to me was the carb temp; the Ford was 105 while the Chrysler was 100. Both showed a temp drop of 20-30* from one end of the muffler to the other. I was not seeing any reason to assume trouble with exhaust flow so I did not remove them.

I'm ready to throw in the towel. I see two options to get this engine running: take it to a pro shop and pay them who knows what it might cost to let them figure out what's wrong with it, or else pull the engine and fully overhaul it. I just want to KNOW what it is. Can you imagine how terrible it would be to install a freshly overhauled engine and be right back where I am now?

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

Just having a guess and not sure what it would do, but it sounds like you may have covered everything else. Could cam timing be out, and making it run like s__t

It might help to understand what is going on if you can give more specific information. I have nerver seen an engine that had the same manifold vacuum reading if the RPM was constant but the ignition timing was changed. If I understand your other posts the manifold vacuum on your car is 20 inches and rock steady until just before it dies.

Can you put a manifold gage on AND a tach AND a timing light and take a series of reading starting from a cold engine and then advancing the timing in stages until you have the 27 degrees that you find works best?

With the vacuum advance disconnected and the dist timing at 10 BTDC the engine RPM is ----, the manifold vacuum is----, and the RPM is---? Do this every five degrees of dist advance AND POST THE NUMBERS. It should be very interesting. Pete