VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1933-1936 Carburetor "cough"

My '36 has a 569S carburetor which is supposed to be the best running Carter W-1. It runs great most of the time but after sitting for let say a month it develops a gag or cough as I call it when accelerating from a standstill even when the car is warmed up.. If I pull out the choke it will not cough so it is not getting enough gas it seems. Anthony Palazzo helped me take the carburetor apart and clean the jets and it ran fine for a while. I just took it apart again and it looks really clean. My fuel filter looks clean. I would just like to know what is causing this. Is there any particular jet that can be cleaned out with the carb on the car? Or do I have to remove the Carb every time this happens?

Is the heat riser free and working?
Try advancing the timing about 5 Deg. with the octane selector.
Is metering rod adjustment correct? done with a gauge.

Also if the inlet or outlet check valves in the carburetor are not working properly they will not keep gas in the accelerator pump passage.

If gasoline dries out in the accelerator pump jet it can plug the passage. The hole is ~ 0.025" and easily plugged by polymerized gas. You can check to see if the accelerator pump is working and jet is open by taking off the air cleaner and looking down the throat while operating the throttle lever. You should not have much resistance and see a small stream of gas squirted into the throat. Be sure that the float bowl has gas in it. If the float bowl is empty the accelerator pump jet won't have gas to squirt.

Thanks guys. I will pursue these suggestions. I know this will be difficult to describe but where are the inlet and outlet check valves for the accelerator pump? It is logical that they exist but I didn't see them.

Look for a big slotted brass cap in the carburetor body. Remove that cap and the inlet and outlet check valves are under the cap. There should be a strainer in there too.

Thee inlet and outlet check valves are behind the large screw plug under the float bowl where it joins the body of the carb.....they came a carb. kit and were always replaced doing a carb. rebuild years ago.

Wow. That was easy. Both check valves were there and the strainer too. Everything looks so clean. It is a mystery. Boy were the check valves tight. It must have been a gorilla that tightened them.

The check valves may look OK but they could be bad. Should be replaced .

I don't have a metering rod. I could probably make one. What should the fuel height measurement be in the bowl?

If the vehicle is sitting for a month, that means (probably) that the fuel in the tank also sits for a month, and goes bad.

It would be interesting to see how the vehicle would run after you had the problem, if you disconnected the fuel tank from the fuel pump, and connected a portable marine tank with fresh fuel.

As to the check valves, genuine Carter valves were an encapsulated ball. Less than genuine Carter used an encapsulated fiber valve (similar to a fuel pump valve, but much smaller). While I concur with all that have posted that these SHOULD be replaced at each rebuild, the genuine Carter don't give a lot of problems, other than sticking from dried fuel.

The function of the accelerator pump may easily be checked by first starting the engine (you now know there is fuel in the carb), stopping the engine, removing the air cleaner, holding the choke butterfly open so you can see inside the choke area, and working the throttle to wide open. You should see fuel coming from the pump jet.

And LOTS of "carburetor problems" turn out to be dead fuel, especially if you are blessed with the alcohol mixture. And while others may have differing opinions, I have tested all of the name brand stabilizers in my own engines with zero positive results. They do have a benefit of helping me to lose weight (but it is from my wallet, not me )

If you can, try the fresh fuel approach.

Jon.

Thanks Jon (carbking) I appreciate your advice and humor. I installed the carb and it is running better now. I will fill with fresh fuel and try to run the car once a week. Anthony Palazzo says that works for him. A side story: About 65 years ago I put a 216 ci in a '33 chevy. with a Rochester carburetor. That carb had the same cough. I got an adapter and put on a two barrel Ford carb. I think it was a "94". Also had Fenton headers and dual exhaust. I could beat any 50 Chevy in a drag race. That Ford carburetor never gave me any trouble (OK Chevy guys close your ears) and I would do the same to my current '33 chevy if I could find the parts.

Regular gas with ethanol does not age well.
Do you have 93 octane in CA without ethanol?
I always put 93 octane in my old cars if the gas is going to sit for awhile in the tank, or ethanol-free 87 octane when I can find it.
If I'm out on the road and going to run through the whole tank of gas within 24 hours, I use the cheaper stuff......

KB - the change in performance that you experienced a few years ago was likely due to two items: (1) a poorly functioning Rochester B (yes, Virginia, the B's do have their issues), and (2) the Fenton headers and dual exhaust.

Replacing a correctly sized and properly functioning single barrel with a two barrel and a 2>1 adapter will virtually always result in WORSE performance, not better. The hole in the intake manifold is the limiting factor. If you watch NASCAR, think restrictor plate! The two barrel may work better if you rework the plenum in the manifold to allow the carb to be bolted directly to the manifold, but not through the adapter, but only if the single barrel was too small for the engine. Remember in modifying an engine that math and physics are your BEST friends!

Have done LOTS of testing with 2>1 and 1<2 adapters. None of the testing showed improvement,

The 569s W-1 is a really good single barrel. We have sold hundreds of its cousin, the 574s, for use on lots of different engines, including a set of 2 on a V-12 Cadillac!

If you REALLY want to make the swap you mentioned, the parts are readily available. But if you do, I would suggest running three timed zero to sixty runs (average the times) both before the swap, and after the swap, and then you will probably decide to swap back

Jon

"If the vehicle is sitting for a month, that means (probably) that the fuel in the tank also sits for a month, and goes bad."

Jon,

When you say it "goes bad" do you mean it is not as good as it was the day it was bought or do you mean that it will no longer run in an engine? What would be the symptom of gas that has "gone bad"?

Thanks!

Ray W

Will try this one without writing a chapter in a book.

Gasoline is a compound of many individual components. Some of these vaporize at lower temperatures than others. Over time, the components that vaporize at lower temperatures tend to vaporize and disappear, leaving only those components that vaporize at higher temperatures. When this happens, the engine can be exceptionally difficult to start, and may not run until the engine is at normal operating temperature, and then not well. Sometimes, idle is impossible without the choke being 1/2 or more engaged.

My experience has been that high compression engines will at least run on the stuff (but often ping), because they generate more heat than lower compression engines.

And there is a lot more chemically that is taking place, especially with ethanol diluted fuel.

Jon.