VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 Stalls after starting when I push down on the accelerator

No problem starting the vehicle, however when I push down on the accelerator the vehicle stalls. If I do not push down on the accelerator and let it run for about 5 to 10 minutes the stalling goes away. Any comments would be appreciated. Thanks for your help.

Chock. Pull it out some or let it warm up,

Best,

Charlie

Thanks for your quick response. Relative to the choke I have pull it out but maybe not enough. Relative to a 1931 Chevrolet that I own, I do not have this problem.

Remove the air filter top, have someone press the gas pedal while you look down the bore of the carburetor. If you don't see a vigorous stream of gas squirting into the bore it's the accelerator pump. It's especially important with a cold engine. Less so as it warms up.

A bit more information would have been helpful:

Here is what I think I know:

From your username, this would be a 1939 Chevrolet, which should have a Carter W-1 420s.
When cold, engine stalls when you attempt to accelerate from idle
When warm, engine does not stall

Guessing:

Since the stalling goes away when warm, the accelerator pump is probably good, but the test Tiny suggested will confirm deny.
Quite normal to use the choke for driveability for a few minutes when the engine is cold.

I would suggest just pulling the choke maybe 1/3, maybe 1/2 (try it) until the engine is warm. Think this will solve your problem.

Contrary to popular belief, the accelerator pump is NOT necessary to drive the vehicle, it is just a convenience. 50 years ago, we saw LOTS of WWII carburetors that had the accelerator pump REMOVED from the carburetor. Gasoline was rationed; the farmers, at least in north central Missouri, didn't wish to waste what gas they had.

Jon.

Thanks for your detailed comments. Sorry i forgot to identify the vehicle which is a 1939 1/2 ton pickup. I will follow your suggestion regarding the choke.

The manifold heat riser may be rusted and stuck in the warmed up position.
VERY COMMON

I am still trying to figure out the problem with my 1939 chevrolet pickup. Basically the truck will start, but once I push down on the accelerator it stalls, After pulling the choke out and in several times for at least 10 minutes or more it will eventually run but sometimes backfire when running and quickly pushing the accelerator down, The possible problems that I thought could cause this to happen include 1. the accelerator pump, 2. vacuum advance, 3. faulty fuel pump and 4. bad carburetor. Can anyone give pinpoint what my problem may be and what i can do to fix the problem. Thanks for your help.

Maybe I am misunderstanding your starting process.

The choke cable controls a butterfly valve in the carburetor. When the choke butterfly is partially closed it restricts air flow which makes the fuel-air mixture richer. A cold engine needs that richer mixture to start and run.

The choke is not a pump so pulling it out and pushing it in does not inject fuel like an accelerator pump. Closing the choke (pulling it out) makes the mixture richer. Opening it (pushing it in) makes it leaner.

When I start my '37 cold I pull the choke out about 1/3 of the way. I also have the hand throttle out just a little to give a higher idle speed. After it starts I let the engine run about 30 seconds before I try to drive the car. After I have driven about 3 to 5 minutes I push the choke in about half way. After about 7 or 8 minutes I can push it in completely. I also push the hand throttle in as the engine warms up.

If I push the choke in too soon and the engine is not warm enough it will stumble when I try to accelerate.

The old 216 was often called a cold blooded engine and features must be working as intended for cold engine or cold weather operation.
Carburetor metering rod and accelerator pump linkages must be adjusted properly.
Manifold heat riser must be free and thermostatic spring have proper tension.
Timing must be advanced as far as possible....too far will result in in starter tuning over hard.

Proper us of choke. Pull choke button out all the way for a cold engine start and push back in about 1/2 way as soon as engine starts. for the next 5 minutes or more of driving slowly push choke in and avoid jaming down the accelerator pedal too fast,
Use the lowest octane gas available AS THE ENGINE WAS DESIGNED TO RUN ON FAST BURING 60 OCTANE GAS. HIGER OCTANE HAS NO MORE "POWER" JUST BURNS SLOWER.

I agree with everything Gene says above about the use of the choke, with this addition...
I've driven six cylinder Chevrolets my whole life. Mostly medium duty farm trucks etc that are heavier than cars to start with and much heavier when loaded.
They have working accelerator pumps.
Still... it's pretty much standard procedure to make the first few shifts with one hand on the choke with a cold engine. Especially during cold weather.
Even with the choke out enough to run properly between shifts... when you open the throttle after a shift you are going to need to pull more choke for a few seconds to prevent a stumble and maintain full power to keep up your momentum/acceleration.
A few minutes later... everything works just as it should with no choke

I should add...
I don't like using any more choke than necessary to keep the engine running steady and making power.
With today's gasoline, an over rich mixture from excess choke seems to put a deposit on spark plugs that soon shorts them out and can't be cleaned off.

Thank you all for your valuable opinions and advice advice. The recipe that appears to work the best was the following. Pull the choke all the way out and as soon as it starts push the choke half way in and pull the throttle out about half way. Then let the truck run for about 5 to 10 minutes. After the temperature dial approaches 180 push the throttle in and the accelerator pedal can be pushed down without any hesitation, stalling or backfiring. I would like to point out that the temperature in my garage when I did this was about 30 F and the temperature the previous night went to about 20F. Of all the cars, Model As, V-8s and a 31 chevrolet that own the 39 truck is without question the most cold hearted.

My experience is that the engine warms up a lot quicker if I drive the car gently. After no more than 5 minutes of driving I can push the choke in completely.