Troubleshooting this problem has gotten a little tricky, so I thought I'd see if you guys could think of some angles I haven't covered to sort it out quickly.



the background: re-ringed the engine very recently. I initially ran it from a gas can assuming the tank to be full of rust and debris. The tank had had a few gallons of very old gas in it. It was so old that the engine would die rather than burn it. I drained that gas and inspected the tank through the sender hole; it appears to have some kind of liner inside of it but no sediment. I put about 6 gallons of new gas in the empty tank and hooked it up to the fuel pump with a filter before the pump. It ran great, would idle very low very smoothly. Having set the ignition up the way I wanted, I was going to rebuild the carb, but though it ran fine, the fuel smell at the carb smelled more like old gas than new gas. So, rather than rebuild the carb just to potentially gum it up, I decided to fill the tank with fresh gas and a can of gas treatment and dilute the residual fuel varnish out. Once I smelled the right fuel smell at the carb, I'd go ahead and rebuild.



I moved my attention on to sorting out other minor issues, which involved a lot of test drives within the neighborhood (as I didn't have the car registered yet). One day, as I'm returning home to park, the engine starts struggling to maintain idle in gear. It has been this way ever since. I have to hold the throttle up to keep from stalling, and even the idle in neutral or park is not the buttery smooth thing it once was.



Things I've checked: 1. The ignition settings. Dwell angle is 27, initial advance is 6, same as when all was well. I watched a timing light strobe with the pickup on the coil wire while idling to see if spark hiccups correlated to engine hiccups, but there was no irregularity in the spark signal. Consequently, I don't think this is an ignition problem.

2. vacuum leaks: I sprayed water all over the manifold gaskets, carb gaskets, and throttle shafts looking for a change in running or the telltale slurping noise of a leak, but none has turned up.

3. Carburetor: it's a Carter AFB so there's no power valve or secondary idle circuit. I took the carb fully apart and went through all of the passages and adjustments. I found no debris or blockages. Special care was given to the idle circuit. No improvement came of this.

4. Valve adjustment: set at .020 cold.



Other observations/notes: When I took the carb off yesterday for cleaning, the intake passages were lined with a tacky varnish which was not present inside the carb but was present on the underside of the throttle plates. Before the test drive that ended with this problem, I made two adjustments: I adjusted the dwell from 25 to 27, and I turned the idle mixture from 2+ turns out to about 1.25 turns out. Last time I had checked the mixture adjustment it had not been possible to run the engine at 1.25 turns; I attributed this change to the fresh new gas working its way through.



Sorry this post is so long, but I like to cover the scenario as clearly as possible. Now, my theory: I am wondering whether this mysterious 'Valucraft Gas Treatment' I added might be the cause of my problem. The product literally did not indicate what its intended use was or in what way it treated the gas. Someone gave it to me one day and I assumed it was for stabilizing fuel so that it would not gum up over longer storage. I added it thinking it might help clean up the fuel tank. Since reinstalling the carb, I found I had to turn the mixture screws out to around 2 turns again to get the best idle, which is not nearly as good as it used to be. There are two things I want to try: 1. running the engine from a can of fresh gas and 2. putting a vacuum gauge on the intake pre-vacuum-pump to look for signs of mechanical mischief.



Can you think of anything else I could be dealing with here?

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

Maybe there's so much gunk comming thru that the filter is partly plugged? Worth a look?

Paul

this is just a thought

you said the tank had some kind of liner,i assume you mean a slosh around type sealer. the earlier ones were not ethanol resistant and if you've topped up with ethanol it may be dissolving the old sealant.

good luck

stuey

UK 

The Carter AFB does have power valves.  They are the two pistons resting upon a pair of springs and they are connected to the metering rods.  Be sure the vacuum ports on the bottom of the carb that feed the power valve pistons are open or exposed to the carb plenum.  Also check that the pistons themselves are working freely.  A bent or damaged metering rod can play havoc with power valve operation.  Pay particular attention to the small air bleed holes in the fuel discharge assemblies.  Beyond that I’ll suggest changing out the fuel again.  And this time checking the ethanol content and insuring it’s 10% or less.  And use premium fuel if you’re not already.

Lorena, Texas (South of Waco)

ok, now I'm extra frustrated/stumped. It seems I've been dealing with at least 2 different problems simultaneously.



First, after going through the carb, the new base gasket I used was misaligned just enough to bleed vacuum to the secondary diaphragm. as soon as the secondaries cracked open, the engine would stall. I found that problem and took care of it, and was able to get a nice smooth idle again. I thought I'd found the problem...briefly.



Second--shortly after dealing with the secondary problem, as I let the engine idle it would suddenly die. Even though I felt confident at first that none of this was an ignition problem, with the secondaries firmly shut the only cause I could imagine for "sudden death" was an ignition component dropping out. I replaced first the condenser, then the coil. The points test ok consistently and the timing/dwell adjustments remain in spec. Yet the trouble persists.



Most of the testing I did was running the engine off of fresh premium gas, so the fuel is not the problem. I verified that the fuel pump is moving plenty of fuel through the filter, which means the fuel supply system is OK.



The current symptoms are: generally very nice idle can be achieved, sensitive to mixture screw adjustment (prefers 1.5 turns out). Occasionally, there will be intermittent random misfires. Idle quality deteriorates below about 600 rpm. After running for a while, the engine WILL DIE randomly. It will fire up immediately after dying but will fail to continue running unless revved immediately. Then, it will run a relatively short time at idle again before dying. Applying the brakes or turning on the lights adversely affects idle quality. It will not idle in gear. I will also note that the resistor tests at 1.6 ohms.



I just don't get it. Before that one test drive, it would idle at 500 rpm all day long no sweat, and of course it could run in gear. Just not sure what else could be happening here.

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

Here’s a shot into the dark.  Your charging system may be the culprit which could be limiting the ignition voltage at low rpm.  The misfires you mention are a clue to this although it could be the idle mixture set either too rich or too lean also doing this.  I would suspect too lean over too rich if picking one or the other based on what you’ve already mentioned.  But you have a number of clues pointing towards the charging system or system voltage at this point.   Check the charging system voltage or output at idle and then the voltage with the engine running faster.  If you see a significant difference, then direct some attention towards the charging system and/or battery.

Lorena, Texas (South of Waco)

Thanks Ted. Tomorrow I'll check that out. I also need to spend some time with a vacuum gauge. I have not attempted to adjust my timing at all so far because it hasn't changed (that I can tell) from when things were working properly, but tomorrow I'll throw that into the mix as well. Updates will follow!

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

This is a long shot in the dark. Several years ago,I had an intermittent problem not unlike yours. All the ignition looked good, and I spent my time on the carbs. Finally, I was running up the idle while the timing light was on, and the timing got real erratic. I hooked up the dwell meter, and got similar results. A new set of points was hanging up on the pivot point, and while they worked fine at idle and just over idle, they'd hang open at higher rpm. Apparently the shake as the engine died knocked them loose. I'd never have found it, but I went back to set them with a feeler gauge, and while I was bumping the motor over with a remote button, they stuck open. Took me a minute to realize they were open and not on the cam. Changed points, problem gone. Really weird, but I saw it happen.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

You say applying the brakes causes it to stall.  Do you have power brakes?  If so, maybe there is a vacuum leak in the power booster.  If no power brakes, then the brake lights may be pointing to a charging problem as Ted suggests.

John - "The Hoosier Hurricane"

Miker, that's a strange one! I'm thinking my issue is similarly strange, but points operation has been very consistent by every measure I have.



Hoosier, I should have specified that I have manual brakes.



So, more info. First of all, manifold vacuum is excellent. I get 20-22" with no major fluctuation, even down to about 550 rpm. This morning it was cold outside and the engine was running awesome as I fired it up and let it run. I ran it off of fresh gas again just to keep that out of the loop. I could idle it smoothly as low as 550 or so but it was happier at 600+.



I ran it for a long time with very smooth and consistent behavior. I even tried putting it in gear, and guess what? It stayed running! But that proved to be an isolated incident.



I checked the voltage at the battery. anywhere above about 700 rpm the voltage was about 15.75V. Around 600, it was about 14V. At 550 rpm it was a little under 13. It was always higher than resting voltage with the engine off.



I reset my initial timing to about 12*, which increased engine speed and vacuum. I noticed that I'm getting mechanical advance pretty early, around 700 rpm or so. Mixture was happiest still at 1.5 turns out.



Anyway, after a good 30-45 minutes or more of idling very smooth with no hiccups, during which time I checked all of the aforementioned stuff and made adjustments, things started to decline. There were misfires randomly starting to show up at very low rpms, then even at higher rpms (we're still talking idle range here). It would stall in gear every time, and then, as I described before it would start immediately but die immediately after.



I checked the resistor again and this time it showed 0.9 ohms. As the engine sat a bit that number climbed back up to 1.7 and I never got a read less than 1.6 after that though I tried to reproduce the 0.9. The coil was hot to the touch, hotter I think than it should be given how cold it was but I'm not sure.



So now I'm going to get a replacement resistor and see how that flies. By the way, isn't 15+ volts a bit high for normal running? Maybe that's overheating the coil in time and causing spark to deteriorate?

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