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1963 Chevrolet Impala stalls on acceleration

When I accelerate from a stop, or very low speed, the car stalls. If I’m very careful to give it gas slowly, and NOT LET UP (or it will stall for sure), I can usually keep it from stalling but it’s still dangerous. I’ve taken it in 5Xs to 4 different mechanics. It’s always OK when I pick it up but a month to 6 weeks later it goes back to stalling. It’s a '63 Impala Super Sport (327, 2 barrel) but the years below only went down to 1970. Hope that’s OK. PS This all kind of started after I had the carburetor rebuilt many years ago but that might just be a coincidence.

My first guess is your accelerator pump is improperly adjusted.

You’ll need to find a mechanic that knows carburetors, they’re getting harder and harder to find.

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And what did they do each of those 5 visits?

If your carb was rebuilt many years ago, it probably needs it again. Limited use cars using pump gas containing ethanol will be very hard on old carburetors. The ethanol eats away certain rubber parts. If E0, or non-ethanol fuel is sold near where you live, I recommend you start using it.

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As It_s_Me noted, definitely look at your accelerator pump. Or rather just replace it.

Rockauto has carb rebuild kits for your car. Though they only show 4-bbl kits for the 327 engine, and you say you have a 2-bbl.

They do show a 2-bbl kit for the 283 Rochester carburetor, along with carburetor model numbers that it fits. See if your 2-bbl is a Rochester and see if it’s model number aligns with any for the 283 carb. If so, you’re in luck.

Or, take this opportunity to switch to a 4BBL manifold with a new alcohol compatible carburetor. Replace any rubber fuel lines with alcohol compatible tubing.

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I would be looking at points distributor cap . Rotor, condenser timing and sticking mechanical advance

Are you sure you have a 327? Not a 283?

True, I had a distributor that had the advance jammed, until I discovered the problem, I had to set base timing retarded to get it to run, then very low performance.

Again, an opportunity (reason) to upgrade the ignition system along with carb/manifold.

Here’s a discussion on how to tell the difference:
https://www.chevelles.com/forums/155-2006/110391-283-vs-327-visual-differences.html

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Hmm, what is the wing thingy they mention on that link?

Rib/Wing whatever you call it
283283

327327

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Some of the carbs of that era had a rubbery sheet for the pump’s diaphragm. It could have degraded or ruptured, or maybe just damaged during installation, since you mention that’s when the problem occurred.

We had a '57 Ford with a Holley? two-barrel that had an anti-percolator valve. This was a small disk which covered a vent in the float bowl. When the accelerator was pressed, it was lifted off the vent hole. The disk became stuck to the top of the float bowl and the car had similar symptoms. The fix was to unstick it by light prying. (I was working in a shoe store at the time and always had metal shoehorns in my pocket. I used one to pop the disk free.)

My vote is for an accelerator pump issue. You might remove the air cleaner after allowing it to run a minute or so. Look down in the primary bore of the carburetor and operate the throttle by hand.
You should see an instant stream of fuel from the accelerator pump discharge tubes. If not or if there is a delay in the stream it could be that the accelerator pump check ball is stuck on the seat.

After that one has to wonder about the effect of Ethanol on the carburetor accelerator pump circuits; as in a gummy mass.

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Like Mr @Mustangman i too am very interested in what work was performed and or what parts were replaced that allowed it to run better for a period of time before the problem returned.

I also agree with @ok4450 and strongly recommend that you perform the test he outlined for you… the results are important and i suspect that you will not observe the near instant stream of fuel squirting into the carb when you operate the throttle with your hand. If this is true… its the accel pump, or its adjustment etc…

Riddle me this Batman, once you are past the acceleration from a stop scenario…are you able to floor the accel pedal with the engine responding with power, noise and rpm’s? Did the tranny downshift? Is it able to run hard with the accel floored till you let off? Or does it respond but then fall on its face shortly after? If you don’t know, please add this test to the others you currently need to perform in order to to help us gather the clues we need.

Aside from the accel from a stop, if she ran out of fuel or stumbled later, like a short while after the acceleration event, then that would strongly point to a fuel supply/delivery problem like a mal adjusted float… or a clogging fuel filter or a tired fuel pump not flowing at a high enough rate or not able to make the psi it needs to push thru the carbs maze of channels and orifices etc…

We need the results from OK’s test and we need the info of what if anything was replaced that temporarily cured the problem… eventho it was only for a short period of time.

With that info we can get you much closer to the solution.

It is my guess that collectively, this particular forum has more carburetor experience under our belts than we do with fuel injection… if not its prolly a close race.

Let us know the results of the two tests outlined above and also the parts replaced that temporarily helped the issue for a time, only to return again.

We really need this data

ok4550 wrote:

Thanks OK. I can’t believe I forgot about this accelerator pump test. I’ve used it hundreds of times.
This is definitely a must-do first test.

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Look at the wires in the distributor for the points.

When you accelerate and the advance plate moves in the distributor, a bad wire can shut down the ignition.

Tester

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Still pretty easy to tell if its the accelerator pump but you just have to drive it to tell. Hard to explain but like just starved for gas momentarily. They just use a leather or rubber plunger to pump gas every time you use the accelerator so they do wear and leak. I used to have to replace them between carb overhauls. Fairly simple.

Yes. The condenser wire can rub its insulation off on the vacuum advance plate on some of the point type distributors. I’ve lost track of when GM went to the uni-point distributor which had no wire on the condenser though and I don’t recall ever seeing a 327SS with a 2 bbl.

I guess only us rednecks called them unipoints.

Just my 2 cents, check the vacuum advance. I had a 69 Buick Skylark was bogging on acceleration, it turn out be a a leaky diaphragm in the vacuum advance. I had to advance the timing 5 or 6 degrees on a 1971 Skylark to cure a hesitation. Both had a 350 V8.

Good luck,

Ed B.

According to the '63 brochure, the 327 only came with a 4-bbl carb:
http://www.oldcarbrochures.com/static/NA/Chevrolet/1963_Chevrolet/1963_Chevrolet_Brochure-2/1963%20Chevrolet%20lg-14-15.html