seando

1929 DeSoto Stewart-Warner vacuum fuel pump

Recommended Posts

Hi All,

 

Now that I have my carb balanced and running *great* (thanks Carb King) I seem to have an issue with my vacuum fuel pump, which I thought I had fixed by re-corking the gasket.

 

Symptoms: Car seems to idle fine and will continue to run at idle in the garage. It even draws fuel from the tank in the back. I say this because I have added gas to that rear tank multiple times and I check the level with a wood dowel and mark it's level with the date. That gas is leaving the tank.

 

When I drove her on the road she ran out of gas. Looking at the clear fuel filter in line I could see it went dry. There was fuel in the rear tank. I added fuel to the fill hole on top of the Stewart, it gravity filled the clear fuel filter in-line and voila, she ran me back home. I removed the feed line from the rear tank that connects to the top of the Stewart. It does have suction. I am not sure how much it is supposed to have but it had "some". 

 

After reading previous posts about Stewarts I decided to pull mine and take it apart, again. It is different than what is documented in the previous posts that I saw. Kind of inverted? I am linking a video of me removing and disassembling the Stewart pump. The inner tank appears dry, which is odd because the gas from the rear tank is going somewhere and the car does run continuously at idle. 

 

Any thoughts form the pros? 

 

 

Thanks in advance

Sean 

Share this post


Link to post
Share on other sites

I can't really help on the Stewart-Warner vacuum fuel pump but I had a question . . .

 

Does the DeSoto use the same funky setup as Plymouth where the vacuum for the fuel pump is provided by the oil pump rather than manifold vacuum?

Share this post


Link to post
Share on other sites

Not sure that I`m seeing all of the video, seems that your sound is not syncing with pictures, you`re mentioning springs and levers that I`m not seeing.

 

Nevertheless, the inner tank that you removed needs to be dismantled further, inside is a float/lever mechanism that opens and shuts the little flapper valve at the bottom.

 

A couple of critical items with these bits are 1) the flapper valve must seal properly on its seat, if there are blemishes or marks on the mating surfaces it wont seal and that inner container will not hold fuel like its supposed to, if you have any leakage here you need to polish the joint surfaces with lapping compound to get a proper seal. 2) the correct movement of float and levers connected to the flapper valve are also very important if they don`t function correctly then again the inner tank wont hold fuel. 

 

Essentially the purpose of that inner tank is to keep the outer tank topped up with fuel, the inner tank is subjected to both fuel and vacuum, when the float is down a vac port is open to the main fuel tank, the vacuum created draws fuel into the inner tank and the float rises, at a predetermined point the float rises far enough to open the flapper valve and it dumps the content of the inner tank into the outer tank, which then supplies the carb. Having dumped the inner tank contents the float/ lever mechanism will close the flapper at which point vacuum starts to draw in more fuel and the process is repeated.

 

So long story short, check float mechanism and flapper seating. You can, with the inner tank removed and held over a suitable container, pour fuel into the inner tank and check its function, what should happen is the fuel will rise to a certain level and the flapper open and dump its load, at least you have determined that this part of the system works, keep an eye on the flapper valve that it remains dry until it opens. 

Share this post


Link to post
Share on other sites

@ply33 this Desoto pulls the vac off the manifold.

@hchris let let me check the video quality again. It should be showing me taking the inner float mechanism out of the inner chamber. Instead of being a sealed metal float like the diagrams in earlier posts it is 3 corks, stacked on top of each other with a center rod piercing them. And as you say, as the fuel in the chamber rises the cork stack rises and open the bottom valve. As cork stack drops the valve closes.

To my eye that bottom valve is really clean and makes a good seal.

Looking at the cork stack and chamber again I do not think fuel is getting inside the inner chamber.

Will perform the test you mentioned. 

Share this post


Link to post
Share on other sites

Yes the float is cork.

 

Have you removed the inner tank and filled it as I explained, will it hold fuel until the float rises and opens the flapper valve ?

Share this post


Link to post
Share on other sites

Oh and by the way its a Kingston brand vac pump that you have, not Stewart Warner, hence the difference in construction of the internals.

  • Like 1

Share this post


Link to post
Share on other sites

In an earlier post, a gentleman suggested temporarily patching in a length of clear line between the vacuum tank and the fuel tank in an easily visible location. This would take some of the mystery out of the situation. You could watch the vacuum tank running through its cycle (or not). Seemed like a good idea. 

Share this post


Link to post
Share on other sites

I had a fuel problem on my 29 Chrysler that drove me crazy for a while. Several times I blew compressed air back in the line from the vacuum tank to the fuel tank. Back out on the road it would run out of fuel. I finally found a piece of rust in the brass fitting at the top of the tank that connects to the fuel line. It acted like a flapper valve to shut off the fuel flow while driving. It sounds like you could have a similar problem with a blockage in the line.

Share this post


Link to post
Share on other sites

Update: This morning I tested the inner tank per @hchris recommendation. Filled inner tank and then released drop valve. It did hold gas and then dump its contents. I did not fill it to the point the cork would rise and dump. When I get a better test setup I will. I do think it was not even getting gas inside this tank because it and the cork were dry when I took them apart.

Next I connected my brake bleeding vacuum pump to the fuel line that feeds the Kingston from the rear tank. It pulled gas straight away. I seem to have movement in both directions by blowing in through to the back and manually vac gas through the line. 

Next, I will connect the outer tank so it acts as a reservoir for the carb. Add some gas into it so I can run the engine and test to see if I have suction on the line from the manifold. 

I will be taking the floats out again and see, now that I know gas was inside there, what does it look like. I need to cut a new cork gasket for that fitting anyway. 

 

@ch1929 - Brass fittings are free and clear. No rusty flapper valves here. That is quit the find you had there. 

 

I will try to video the tests so y'all can see my testing protocols. My intent is to preserve this car as best I can. She is a survivor and deserves that. I know I can get this Kingston pumping again. 

 

* how do I edit the title of this post? I had Stewart on the brain but it is a Kingston as @hchris said. DOH!

Desoto tests.mp4

 

YouTube:

 

Edited by seando (see edit history)

Share this post


Link to post
Share on other sites
2 hours ago, seando said:

. . . and test to see if I have suction on the line from the manifold. . .

 

 

So Chrysler did the vacuum feed differently on DeSoto than they did on Plymouth? Seems odd as their engineering department usually used the same or similar solutions across the various makes.

Share this post


Link to post
Share on other sites

I snuck out to the shop during lunch an did another test of the inner tank closer to what @hchris described. On first pass the can holds the fuel tight. At the appointed level the flapper valve on the bottom appears to open and fuel drops. It is at this point that the flapper valve may not be going back to a tight seal. Fuel continues to trickle out the flapper valve. I jossled the inner tank and it appears the fuel stops trickling, then dumps again and then trickles again. After the video ends I opened the flapper with a screwdriver and the contents dumped.

First things first, will polish joint surfaces per @hchris 

 

Share this post


Link to post
Share on other sites

Got out for another quick test on the suction intake off the manifold. Definitely has suction, enough to keep my finger stuck to the pipe. Once I break the suction the car comes close to stalling.So by process of elimination my issue most likely is in the inner can's floats and valve. 

 

 

Share this post


Link to post
Share on other sites

If the inner tank has a flapper valve on the bottom, I suggest you test whether it is sealing by pressing the empty inner tank part way down into a bucket of water. The flapper should hold the water out with minimal leakage. If not you'll need to check on why -- pits on the sealing surface, warped components, etc. This sealing action is important in preserving the vacuum so that the system draws fuel from the gas tank. 

Share this post


Link to post
Share on other sites

Desoto,s used both tanks.I will check my books closer this weekend,The one I just rebuilt was a early 28,with a stewart tank,Maybe consider changing it over to the stewart.If you need parts for the Kingston,i have some,we have no dies to rebuild them.

Share this post


Link to post
Share on other sites

Well done and an excellent portrayal of what I was trying to describe.

 

Its crucial that the flapper valve seals as you can see, without proper sealing you will have neither vacuum action or fuel input. Even a minor leak at the valve will cause fuel in the inner tank to be depleted faster than vacuum action can replace it, which would explain that whilst  it may idle well, take it out on the road and the demands will outstrip supply, and of course once the engine stops so does the vacuum.

 

So from what I am seeing your problem is somewhere in that valve/linkage mechanism, not ignoring the fact that some wear and tear on the links which hold the valve may be causing it to seat askew and not seating properly.

 

Keep up the good work, you are not only fixing your own problem but providing valuable information for others out there on what is becoming a lost art in vac tank analysis. 

  • Like 1

Share this post


Link to post
Share on other sites

Thanks for the positive words of encouragement.

I am going to point the finger at the bottom flapper valve. I took it apart and polished up all components and seals with 1500 wet grit. Recut cork gasket. I performed the test @Jbartlett described with the bukcet of water. No leaking at all. Perfect! 

Then did the gas test again. Holds great then dumps. Ok.

Then it keeps trickling. And trickling. Fiddle with the flapper ever so slightly and it stops. 

So, I will look at trying to tighten it up but what do we think about making a small gasket for the seal between the flapper and opening? 

20180228_181203.jpg

Share this post


Link to post
Share on other sites

No, definitely no gasket between the two flapper faces.

 

I would be inclined to put it back together, refit and test drive, see how you go.

 

Put some fuel in the outer tank first,  just to get the engine running, and then see whether it can keep up

Edited by hchris
add words (see edit history)

Share this post


Link to post
Share on other sites

You don't want a gasket between the flapper surfaces. As soon as the gasoline level rises in the inner tank and pushes up the cork floats, they shut off the vacuum from the engine -- and that enables the gasoline to drain through the flapper valve into the outer tank, which supplies the engine. Then the process starts all over again. The floats drop, opening up the engine vacuum into the inner tank. The vacuum causes the flapper valve to close, sealing the inner tank from the outer tank and allowing the vacuum to pull fuel up from the gas tank. That's why the flapper valve has to seal effectively under vacuum -- and not at all when no vacuum is present.

Share this post


Link to post
Share on other sites

I have never worked on  Kingston tank/pump, or any of a few other brands of vacuum type fuel pumps, only the Stewart Vacuum tanks. Those I have had a few cars with. Most have given me some trouble. Most gave a lot of good service once a few age bugs got worked out. I don't know about the specific issues a Kingston may have, but as it appear to be similar in concept to the Stewart,  I suspect they are similar.

The flapper valve on your tank is quite different than the Stewart. It is more complicated, but could be better, or not. I like the Stewart's simple flapper valve. However, the concept is the same. And in reading through all the comments, I see one detail that needs to be clarified. And this would be true for both the Stewart and your tank.

That flapper valve, and its fit, is more critical than would be expected at a quick glance. More than simply not working efficiently if the flapper valve leaks (even a tiny amount)? If the flapper leaks at all, when the upper tank valves switch vacuum into the inner tank, leakage will cause the inner tank (upper chamber) to suck gasoline back up from the outer (lower) tank. IEven a small leak can make it become the path of least resistance as the gasoline is only a couple inches away as opposed to the gasoline tank about eight feet of small tubing and two feet elevation difference away. Even if the leak is minor enough to not actually lift the gasoline in the lower chamber up? It may be enough to cause the gasoline in the lower chamber to NOT drop into the carburetor. Gasoline doesn't drop into the carburetor, engine starves for fuel and dies. Vacuum ends, fuel then drops into carburetor and you get to wonder why it won't run when it has gasoline (had a warped flapper on a Stewart tank once, drove me nuts for a couple hours).

 

Something else that helps confuse the issues. Engine vacuum pressures, and fuel consumption rates, are NOT mutually consistent. Vacuum is fairly high at an idle, and goes down as the throttle is opened up. As the car is driven, higher speeds, coupled with loads, increase fuel consumption. So, the way it works out, is that with a vacuum tank, it tends to work least efficiently when you need it the most. But this is also why it may work fine, sitting in the shop, at an idle, but then fails to work going down the road, even at maybe fifteen or twenty miles per hour. The engine needed more gasoline, while the weaker vacuum was holding the gasoline back from the lower chamber and not drawing enough fresh gasoline from the rear gasoline tank.

 

Regardless all that. The vacuum tank was an incredible work of design and technology for its day. For about fifteen years, more cars (other than Fords) had them, than did not. They solved several minor safety and convenience issues of the time and made it practical to put the gasoline tank away from where the passengers sat. It took materials technology that did not exist in the early '20s to make the mechanical fuel pump a practical reality. With just a little effort, a vacuum tank can still be a practical and reliable way to feed a gasoline engine.

Driving a car with a nicely working vacuum tank is a personal victory most people will never understand. That is my silly opinion.

  • Like 3

Share this post


Link to post
Share on other sites

The outer tank is not subjected to vacuum at any time, it simply serves as a reservoir for the inner tank to dump into. This is quite different to the Stewart design where the whole of the container is subject to vacuum and needs to be perfectly sealed to function.

 

The Kingston has an inner tank and this is the only area subject to vacuum and only when the flapper valve is closed. The vac line (from manifold or oil pump depending on make) is connected directly to the inner tank and causes fuel to be drawn in, under vacuum whilst the flapper is closed. As the fuel level rises in the inner tank a float (connected by linkage to the flapper) rises to a given point, the flapper is opened, fuel is dumped to the outer tank (reservoir) and vacuum lost, as the inner fuel level drops, the float moves to close the flapper and vacuum is resumed drawing in more fuel; this cycle is continually repeated in order to maintain a head of fuel in the outer tank (reservoir) which then gravity feeds to the carb.

 

I much prefer the Kingston design over the Stewart as its far less complex,  with none of springs and levers and cast upper lid that give so much grief on the Stewart. 

 

But for sure, the down side to all of the vacuum systems is diminishing vacuum as the throttle is opened, some manufacturers designed various boosters or enlarged reservoir tanks to offset this problem, but if the hill is big enough don`t be surprised if the engine quits.

Share this post


Link to post
Share on other sites

It sounds like me riding a bicycle. Every hill becomes a challenge.

Looks like I am rained out today so I may fiddle with the flapper and try to get her to seat tighter. One test I may perform; if I add a washer to the top of the inner cork stack will that give it just enough additional weight such that the flapper closes with a little more umph and tighter seal. But not so much weight that the corks don't rise. To the naked, or even spectacled eye it looks "tight". 

20180301_100655.jpg

Share this post


Link to post
Share on other sites
10 hours ago, wayne sheldon said:

. . .

Something else that helps confuse the issues. Engine vacuum pressures, and fuel consumption rates, are NOT mutually consistent. Vacuum is fairly high at an idle, and goes down as the throttle is opened up. As the car is driven, higher speeds, coupled with loads, increase fuel consumption. So, the way it works out, is that with a vacuum tank, it tends to work least efficiently when you need it the most. But this is also why it may work fine, sitting in the shop, at an idle, but then fails to work going down the road, even at maybe fifteen or twenty miles per hour. The engine needed more gasoline, while the weaker vacuum was holding the gasoline back from the lower chamber and not drawing enough fresh gasoline from the rear gasoline tank.

. . .

 

Which is why I've asked twice on this thread if his DeSoto used the same mechanism as Plymouth for getting a vacuum source. On the Plymouth of that era the vacuum for the fuel pump is provided by a tap off the suction side of the oil pump. So the faster the engine is turning over the more vacuum you have, totally independent of carburetor throttle position or engine load. So far, if that question has been answered I haven't seen it.

 

Down side of the Plymouth (and I would have assumed all other Chrysler built makes) is that if something goes wrong with the vacuum fuel pump you could lose oil pressure by sucking too much air.

Share this post


Link to post
Share on other sites

Takes vacuum off the intake right above the carburetor. The video is not great but I posted earlier about the manifold vac test and tried to get the camera angle as best I could showing this connection. 

Share this post


Link to post
Share on other sites

I don't know if this has anything to do with the flapper issue, but those floats look to be well past their sell by date. Are they indeed "floating"? Zeke

Share this post


Link to post
Share on other sites

definitely floating, but i thought the same thing. If they didn't float they wouldn't open the flapper to dump fuel. But that is why I pondered adding the washers for counter weight in case the cork's mass had deteriorated over time. 

 

I have got it to the point where it will dump, slow trickle and stop releasing fuel. Then with more fuel, dump again, slow trickle and stop. I am not sure if the trickle is self induced from the dump splashback, or the cork raising and closing the flapper. Is it slightly gradual given the level drops and the cork rises, or is it supposed to be a sudden and abrupt stoppage? 

 

Tornado warnings today so the road test will have to wait. 

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...