1950s 1956 Cadillac loses power on acceleration

[jaxops]

This has been slowly developing.  It runs fine for the first 5 miles or so, and then the engine shuts off as you try to accelerate from a stop.  It will restart fine but dies in gear.  My shop at Bruce Warren Auto Repair in Norfolk, VA are checking fuel, ignition, timing, and the transmission.  Sounds like a fuel starvation problem but I could be wrong. More to follow.

[Jeff Rosansky CLC #28373]

Does your accelerator pump work? If so then next time it dies, open the hood, take the air cleaner off and hit the throttle. If it squirts a few times, you have fuel.
I would also feel the coil to see if it's hot, and possibly change the condenser.

[Lexi]

Does it suddenly die, or does it chug a bit before shutting down? Usually fuel starvation related issues cause the car to chug or stumble a bit prior to dying. Is there an odour of gas when this happens? Could be any one of a lot of problems. Clay/Lexi

[TJ Hopland]

Does it restart right away?  Or does it have to crank for a while?   Or does it have to sit and cool then it starts or again has to crank?

[Lexi]

Further to my previous post, a clean out of your fuel line and even the fuel tank might be necessary. Dirt lodged anywhere in the system can cause issues. One might be too much fuel, or a fuel restriction, either one leading to a stall out. Is your carb top bowl gasket wet or damp with fuel? My last carb problem was caused by debris in the needle seat valve. Severe flooding was the result. Check your oil dipstick for signs/odor of fuel. An immediate oil change would be necessary if so.

If your '56 is OEM you either have a Rochester or a Carter carburetor. So, further to Jeff's comment, the accelerator pump on the Rochester, is rather/somewhat easily accesible to change, even with the carb on the car. The Carter, as I recall is more problematic to get at. I also seem to recall that there was this weird pivoting linkage that is accesible up top if a screw is removed from a port cover to reveal this system. Regular maintainence is recommended here with drops of oil on these pivoting shafts which are visible when the top port cover is removed. Think they acuate the accelerator pump or are at least tied into that system. Never worked on one before though, as I have the Rochester on my '56. That area of your carb might need attention, if it is a Carter with those pivoting arms.

As TJ hinted at, inspection for possible heat issues like vapour lock is something to consider especially if you still have your heat riser installed and over time has been seizing. You did say that the problem has been developing over time. Perhaps it now is causing hot exhaust gases to continually flow under your carb? With your carb off you can check to see if in the past someone blocked off that exhaust port/channel in your intake manifold. That would eliminate that, if so. You can also check to see if the heat riser is there, operational, stuck, which if memory serves would be on the header pipe between the exhaust manifold and the pipe-driver side. Clay/Lexi

[jaxops]

Great suggestions all around.
- It does restart right away
- There is good spark
- I agree completely that the fuel lines need a thorough cleanout
- The accelerator pump is a probable cause like you stated earlier

The shop reported that the car is running well so far, but they are holding it for more testing through Monday.
Next week- the results.....stay tuned!

[Michael Petti]

Had exactly that problem years ago on a Dodge. A leak developed between the carburetor and the manifold. Idled fine but step on gas and car died. Might also be an intake manifold gasket leak or a cracked manifold. Let us know what it turns out to be.

[James Landi]

These fuel pumps, famously located on the oil filler where the mechanical fulgrum gets zero lubrication, are subject to a slow and painful (for the driver) death. Because the pump has to do heavy lifting, i.e. creating a sufficient vacuum to suck gas up the tank, along rubber and steel pipes that are subject to cracks, splits, and un-observable vacuum leaks, one can chase the problem and experience great frustration.  If you were to detach the fuel pump and use the palm of your hand to push the lever and run the fuel into a bucket, I suspect you'd likely see air bubbles mixed with your fuel, a certain indication that pin holes exist in the fuel line.  I've had pin holes in the tank pick up, so that the car would run perfectly until the fuel level got below half a tank! Another confounding  challenge with the fuel pump is a worn pivot on the fulgrum that creates just enough lash so as to render your pump WEAK when the pump is hot. There can be zero lash (looseness) or else the pump will fail when the engine needs more fuel in the carburetor. (back in the old days, knowledgeable mechanics would pack the pump casing with grease before installing a new pump).   Hope this helps,   James

[jaxops]

Yes, quite so.  I am replacing the fuel pump as well.  Good point about the air leak.  I did have that before and always worry about it on the carburetor base.  We'll check that out as well.

Thanks to all for the suggestions.  Still working it.

[Dave CLC#16900]

Probably not your issue but thought I would add my experience when diagnosing my '63 Impala years ago.  I had a surge after some time on the highway.  It had a bad pickup in the tank, which was a big part but not all of it. 

What finally fixed it was the external condenser on the distributer, used as a noise suppressor for AM radio.  Once it heated up it was affecting the ignition.  Replacing that fixed it!  I spent a dedicated month working on this.  After going through the entire fuel and ignition system, the problem was a $1 part (in 1988).

[TJ Hopland]

Restarting right away on the fuel side kinda implies something like a clogging pickup in the tank.  Crud gets sucked up to the pickup and clogs it but as soon as the engine shuts off the crud falls off so it can suck again.

Electrical seems more likely for a works then doesn't sort of thing.  Maybe have the shop hook up a manual vacuum pump to the distributor advance and run it through its whole range to make sure the spark stays good.  There could be some cracked internal wire or grounding issues that only fail in a certain vacuum state/position.

[Jeff Rosansky CLC #28373]

When we woke our 55 up, I thought the fuel line was good, but wanted to check it anyway.
I plugged the end at the tank and filled the line with mineral spirits. Then I hit the open end with compressed air. Not high psi, but enough. Held pressure in it for about 5 min. Then I climbed under the car and looked at the fuel line. It was wet under almost every clip. There were small undetectable holes in it.
You may have that issue.
But if it starts immediately, then I'd say fuel is in the carb.
Thinking condenser or coil.

[James Landi]

"I plugged the end at the tank and filled the line with mineral spirits. Then I hit the open end with compressed air. Not high psi, but enough. Held pressure in it for about 5 min. Then I climbed under the car and looked at the fuel line. It was wet under almost every clip. There were small undetectable holes in it."

Jeff's test result is often the case with most very old cars... metal fuel pipe, metal clamp, metal frame ALL somewhat dissimilar metals create the perfect opportunity for galvanic action, that over the decades renders the fuel line useless with very tiny vacuum leaks that are covered by those tight clamps, thus compromising a fuel pump's ability to work. As I've mentioned in the past, even the fuel pick up line in the tank can develop compromising pin holes, so that your car seemingly runs out of gasoline even though the tank is partly full.  Frustrating...

[Jeff Rosansky CLC #28373]

"I plugged the end at the tank and filled the line with mineral spirits. Then I hit the open end with compressed air. Not high psi, but enough. Held pressure in it for about 5 min. Then I climbed under the car and looked at the fuel line. It was wet under almost every clip. There were small undetectable holes in it."

As I've mentioned in the past, even the fuel pick up line in the tank can develop compromising pin holes, so that your car seemingly runs out of gasoline even though the tank is partly full.  Frustrating...

We actually have that issue. Had the tank cleaned and coated years ago, but there must be a pinhole in the pickup. We have issues when it gets below about half a tank.
So, I keep it full.

[jaxops]

It sounds like everyone has had a similar problem with a world of different fixes.

  So, we replaced the fuel pump, checked the timing (somehow the dwell was up so we reset it at 30 degrees). Points and distributor were all firing as were the spark wires. We replaced the spark plugs (dirty but not bad but we went ahead and changed them out).  No air leak under the carburetor.

 We found that the blocking of the crossovers under the carburetor left the choke stone cold.  A copper attachment was put on the manifold up to the choke to minimize the heat we had before but get some heat up there as the car warmed up to auto-adjust the choke. All of the heat riser mechanisms were removed before I got the car, so it was 300 degrees, or nothing. [I'm sure that heat riser system would work fine if it were all there and in working order, but after 12 years of overheating, I can't go back to it]

  Additionally, the carburetor was gunked up, so we are in the process of rebuilding it.
Hopefully this will do it. 

  The car sat a lot due to the 100+ degree or rainy summer, so even though it was rebuilt last year, it's best to rebuild the carburetor again.  Next summer, it will have to be driven and get wet!

Thanks to all for your feedback and advise.  Especially since all of you have had an issue like this. It helped us focus on what to check vice "everything."

[Roger Zimmermann]

The elimination from the heat riser has no influence over the choke heating. I did that recently on my Biarritz.
On the passenger side exhaust manifold, there is a provision for a tube which is screwed at the chocke. The vacuum created by the carb is sucking air heated by the exhaust manifold, heating the choke's coil.
I had a '56 car, unfortunately the car is sold and I have no picture from the system.
I could take pictures from my '56 Biarritz; the provision at the manifold is the same, the tube is different as the car has two carbs.

[Lexi]

Like Roger, I was puzzled by the heat riser comments. The choke tube is separate from the heat riser. I believe I have an extra OEM choke tube meant for a 1956 Cadillac Rochester carburetor, if needed. If your carb is a Carter it uses a different choke tube, (configuration of bends are different). I have one of those as well, but keeping it. Can provide some measurements and photos if required. Heat is transferred from the "hot box" on the exhaust manifold via convection. There is a thin metal plate cover with a hole, that the tube fits in. Two screws attach it to the manifold. Should you or your mechanic decide to do some work there ensure that plenty of soaking penetrant is used for a while, before attempting to remove the 2 screws. Once took me 2 hours to extract and repair a broken one. Clay/Lexi

[jaxops]

So the upshot was that the carburetor was "gunked up" probably from the fuel stabilizer I was using.  The new fuel pump helped, as did the new battery I put in it today.  The car runs fine now.

Thanks to All for the assistance, which I had p0assed along to the mechanics.

[Michael Petti]

Glad you fixed it and thanks for posting the solution. What stabilizer do you use that ginled ip the carb and will you cjange brands?

[Lexi]

So the upshot was that the carburetor was "gunked up" probably from the fuel stabilizer I was using.  The new fuel pump helped, as did the new battery I put in it today.  The car runs fine now.

Thanks to All for the assistance, which I had p0assed along to the mechanics.

Yes, as per Michael Petti's comment, what stabilizer is the "culprit"? Clay/Lexi