seando

1929 DeSoto Stewart-Warner vacuum fuel pump

Recommended Posts

6 hours ago, ply33 said:

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.

 

 

There was that reasoning of constant vacuum with the oil pump source, as to why others relied on manifold vacuum I don,t know but certainly this method was the most popular.

Was there the potential to dilute the oil with fuel if a malfunction occurred ? I don`t know.

Share this post


Link to post
Share on other sites
1 hour ago, seando said:

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? 

 

Yeah I have to agree that the floats look pretty ordinary and perhaps they don`t have enough lift/weight to hold the flapper shut tight, worth a try to add a small weight and see if it makes a difference. One other thought I had, is it possible the corks are slipping on the shaft rather than lifting it ??

 

 

Share this post


Link to post
Share on other sites

Now that you mention it, there is a little play in the washers that hold the corks in place. Just a little. I meant to solder them.

I put everything back in place. Started her up and idled. Weather permitting will road test tomorrow. Will post update. 

  • Like 1

Share this post


Link to post
Share on other sites

Quick update: Started her up and she was purring like a kitten. Let her idle in the garage for 5 - 10 minutes. Then she just died. Lost power and died. Now I need to hold throttle open to keep her running. Gas is in the filter still and when she stalls gas leaks out carb as it is unburned and falling back down. Fouled plugs? Going to get new and try it again. 

 

BTW: received carb rebuild kit from @carbking and it looks awesome. Also got door handles from @thehandleman and they are spot on what I needed. 

 

Little by little. 

  • Like 1

Share this post


Link to post
Share on other sites

Update: 

I tell you she runs like a kitten when the reservoir has gas and the vac tank is out. Ran for 30+ minutes in garage while I tested vac can.

Today's tests. Removed cork floats and tested in bucket of water. Corks float and drop no issues. Connected my brake bleeder vacuum pump to the manifold port on inner vac can. Holds a vacuum no issue. Multiple vac, hold, drop. Repeat. All same. I added a bead of solder to washer holding corks in place on lifter rod. 

I do think that I am getting too much gas in the setup now. With it all together and running she eventually stalled. I disconnected the vac line on top of can and it was wet with gas. 

When the inner can is in the reservoir tank that does make an relative air tight seal, intentional or not? 

With the whole system together gas does not pour into the fuel filter. Rather it trickles. There is a reverse vacuum in the line from the reservoir bottom to the carb. Seems like air gets trapped and prevents gas from pouring into filter. This air bubble cause by gas burning off as she runs may not be bleeding out very quickly from the system because of that air tight factor.

In the picture I have colored and marked the connections on the top ports. Blue goes to windshield wiper. Red goes to back fuel tank. Unmarked is vac line from manifold. I wonder what yellow is? It is a straight pin hole to the vac line from manifold. I have it capped off.

I guess my other question is, if the system is relatively air tight, and the vac keeps pulling and pulling, that would explain fuel level getting too high and back sucking into manifold. Seems like there should be a relief valve? 

Sorry for the brain dump all. Really want to preserve this tank and appreciate the help. Other picture is me trying to listen to the vac in the tank. 

20180302_181938.jpg

20180302_170927.jpg

Share this post


Link to post
Share on other sites

My first thoughts are the carb float/needle mechanism are not shutting off and the carb is flooding, if so this would give you the fouled plugs so i would hold off buying new ones.

 

Possibly this is linked to the fiddling with the vac tank, perhaps now that its working more efficiently you might have a greater head of fuel in the tank, or the flapper valve is not opening and flooding the reservoir. Remove the inner tank and see how much fuel is in the reservoir, I would expect there should only be an inch or two of fuel inside if things are working properly.

Edited by hchris
add words (see edit history)

Share this post


Link to post
Share on other sites

But she runs sooooooooo well. I need to rebuild the carb with my new kit anyway.

 

When I took the inner can out she definitely had more than a couple inches of fuel in reservoir. Inner can still had fuel too. Not 16 oz but some.

Share this post


Link to post
Share on other sites

OK, having read your most recent post it would appear that the inner tank is not dumping and the reservoir is flooding to the point that fuel is being sucked back through the manifold line.

 

If the inner tank cant dump it will continue to fill until the fuel level reaches the top of that stand pipe, in the inner tank, then spill over into the reservoir, at some point if the inner tank level keeps rising it will be drawn back into the manifold through the suction line.

 

The outer tank (reservoir) must be open to atmosphere, thats why the filler port is in the top of it, the only piece subject to vacuum is the inner tank. If the reservoir is full to the brim then there is no airspace in there, hence probably why you observe fuel is only trickling to the filter

 

Cant help you with the yellow port, but I wonder if its also a vent ??

 

Share this post


Link to post
Share on other sites

Maybe i am starting out with too much fuel in the reservoir bottom? Maybe i should start with just an inch? I had been setting it's level to just below the flapper. 

Share this post


Link to post
Share on other sites
1 hour ago, hchris said:

The outer tank (reservoir) must be open to atmosphere, thats why the filler port is in the top of it, the only piece subject to vacuum is the inner tank.

Is this the yellow port - an air vent to outer tank?

Share this post


Link to post
Share on other sites

I found a video on a salvaged 29 DeSoto and grabbed 2 screen shots of the vac fuel pump. Doesn't look like that rear port (Yellow in my shot) connects to anything. 

 

This is why I try to record everything. You never know what someone may be researching. 

stewart cvac2.png

stewart cvac.png

stewart cvac3.png

Share this post


Link to post
Share on other sites

i commend you for your dedication. all the challanges of a vaccum fuel system explains why the previous owner of my 23 buick “lost” the top portion of my unit. i’ve been using an electric fuel pump with a regulator set to one psi to run my car. 

  • Like 1

Share this post


Link to post
Share on other sites

When I had fuel being sucked into the vacuum line, the corks were sliding up on the brass shaft.  The upper "washer" solder had given way.  If the float doesn't rise to open flap, gas will continue to fill to the vac line as hcris said and you experienced.

 

If the bottom "washer" on the shaft has not been adjusted, move the top one down so there is no movement of the corks between these washers and solder well.  If both washers have come loose, it may be trial and error to find the "sweet" spot on the shaft for cork location.  Perhaps your corks are too old, but mine have never been replaced in the 52+ years I've had my car and its never had an electric pump.

 

As ply33 said, my '29 Plymouth vac is from the oil pump; the copper line is not stock.  Here is my set up with the wiper vac from the manifold.

 

Good luck, your getting close to having it working.

 

frank

5a9a370ebb89f_EngineLeftSide1.thumb.jpg.bb6ac97f44164c98cf2b7437990a7bf4.jpg

Share this post


Link to post
Share on other sites
6 hours ago, Spinneyhill said:

Is this the yellow port - an air vent to outer tank?

 

Yes it would appear to be a metered orifice serving as a vent, might be worth taking out the blank.

 

2 hours ago, frank29u said:

it may be trial and error to find the "sweet" spot on the shaft for cork location.

 

i agree, trial and error to get the floats in the right spot is probably the answer, obviously someone else has had a fiddle with these in the past

Share this post


Link to post
Share on other sites

Folks,

 

I don't want to get ahead of myself but I am giddy with excitement. I put the whole thing back together today and was able to idle her in the garage for 10+ minutes, sounding so sweet. I then backed her out and drove her around the block, entirely! Pulled her back in garage (up an incline mind you) and checked the filter. Still has gas showing and same level as pre-drive. Then backed her out again and drove her 2 more times around the block! Previously I never made it one entire swing around the block when I would fill the reservoir with gas. 

I did add a bead of solder to the top micro washer on the inner float stack. That washer had some play. If anyone is reading this in the future, be careful with your solder. If you leave some slop on the center rod it may not clear its pin hole cleanly and throw off the balance by not rising all the way.

Instead of topping off the inner reservoir with fuel after the inner can was in place, as I used to do, I only added an inch of fuel before putting the inner can in place. My working theory is that the excess fuel was causing a back vac in the whole system, allowing gas to back suck into the vac line form the manifold. 

It did stall out a couple times, hard stops and poor clutch work. But a win is a win.

Here is the latest video test on YouTube. I tried to make it complete as possible in case there is another future hackanic who runs into one of these engineering marvels. I say that with utmost respect. It's one of the joys of these cars, deciphering what the engineers were able to accomplish with the technology and resources of their day. 

Special thanks to everyone on this forum who came through with tips and tricks, especially @hchris who seemed to be with me every step of the way. 

 

 

8 hours ago, hchris said:

 

Yes it would appear to be a metered orifice serving as a vent, might be worth taking out the blank.

 

Unfortunately if that end cap is removed it is equal to leaving the hose disconnected from the manifold. When I said "pin hole" I was understating its size. {First time for everything}. 

Share this post


Link to post
Share on other sites

Congrats.

Glad you got it working.

 

Keep driving !!

 

 

Bill

  • Like 1

Share this post


Link to post
Share on other sites

My vacuum tank Epiphany: I was on a VMCCA Nickel tour driving my 1928 Chrysler. I happened to be the last tour car when I got stopped at a railroad crossing on some quiet back road. As I sat waiting for the train to pass, the vacuum tank refueled causing the engine to stumble a bit. Here I was alone with a 60 year old car that wasn't running the best and no one around to help if the old beast died. What was I to do? About that time the train passed the crossing and the vacuum tank refilled causing the engine to smooth out.The crossing guard and lifted I thought to myself "Well, we have gotten this far, let's see if we can make it to the end of the tour. We did. Afterwords I did investigate the vacuum tank to find out exactly how it works and how to fix it. If you are going to own one of these old beasts you had better know how it operates and how to fix it. The "technicians" at the dealership aren't going to be a lot of help. Zeke 

  • Like 1

Share this post


Link to post
Share on other sites

Well done, your perseverance paid off and you have given others a unique insight into the black art of vacuum tanks. 

 

Now go find a big hill and see if you can make it to the top without running out of gas, if you can achieve that go home sit down and have a beer or two. ??

  • Like 1

Share this post


Link to post
Share on other sites

We now must dub thee apprentice wizard master of the vacuum tank! Soon to be Master Wizard Master of the Vacuum Tank.

  • Like 1

Share this post


Link to post
Share on other sites
On 03/03/2018 at 10:09 AM, seando said:

I wonder what yellow is? It is a straight pin hole to the vac line from manifold. I have it capped off.

 

All quiet here so I assume everything is fine, still scratching my head re the unidentified "yellow" port in an earlier thread and then I came across these items, courtesy of the Dodge Brothers newsletter some years back (a gold mine of information for Dodge owners).

 

So its purpose in life is to increase the vacuum force (booster). This enables a greater pulling power for fuel from the rear tank and is particularly helpful for high throttle openings when going uphill etc. which reduces the risk of running out of fuel in the reservoir under such conditions.

vac booster 1.jpg

vac booster 2.jpg

  • Like 1

Share this post


Link to post
Share on other sites

Years ago a club member asked my dad to help him set the idle jet on his car.  Dad set the idle nice and slow and then all of a sudden the engine really slowed down almost dying and dad quickly adjusted the idle a little higher.  With that we sat back and was happy with the idle speed of the engine.  All of a sudden the engine sped up to a faster idle, so dad again adjusted the idle jet to slow it down.  He then looked on the firewall and noticed the vacuum tank and realized when the tank needed refilling, it took some vacuum and slowed the idle.  Yes, your engine will slow down when the vacuum tank is being filled.  Similar to driving up hill in the rain with the wipers on and you have vacuum wipers.  At this situation you may not have sufficient vacuum to run the wipers.  You may have to let up on the throttle (and slow down) to get the wipers to work (or downshift) and then give it the gas to get up the hill.  Understanding what is going on under the hood really helps.

Don A

Share this post


Link to post
Share on other sites

hchris, thanks for the valuable information on that fitting.

 

I wonder why the Chrysler engineers took the vacuum from the manifold instead of of the oil pump like they did on the 28/29 Plymouth?  May be different oiling system on the 6 cylinder vs 4.  Never want for vacuum/gas going up steep hills with this Plymouth setup.  The wiper, on the other hand, comes from the manifold and it can be sluggish, as we all know.

 

 

Oil Pump1.jpg

Share this post


Link to post
Share on other sites

Well it seems the move to change vacuum source from manifold to oil pump came fairly late in the evolution of vac units, so I can only guess this was a means of overcoming loss of vacuum with large throttle opening. It wasn't much later that mechanical fuel pumps became the norm and the problem disappeared. 

Share this post


Link to post
Share on other sites

For Plymouth, the Finer 30U was fitted with an AC Fuel Pump-Series B after car s/n 151757, according to United Motors Service parts book for Plymouth 1928-1934 models.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now