'31 Fuel Issues - Need Help

[CalCadGuy]

I have recently acquired a '31 Cadillac and am working on the fuel system. I have had the Carb rebuilt and the Vacuum tank restored. I have installed both, filled the tank with fuel. Car starts and runs well....then quickly runs out of fuel. I have hooked up the Vacuum pump on top of the manifold, but the system does not appear to keep the car running. Can anyone help with advise? Does anyone know someone who works on the Vacuum pumps...is that my likely issue? Thanks for any help, Marc

[Chris Cummings]

Hi Marc,

As you may already know your vacuum tank depends on the vacuum pump to pull fuel from the gas tank and keep the vacuum tank supplied.  From the vacuum tank forward, the fuel system is gravity feed, like a Model A Ford.  A vacuum tank that isn't getting properly replenished will let the car run fine until vacuum tank runs dry.  Then the carburetor runs dry and the engine stops.

Does your car have the original fuel and vacuum plumbing? (Some cars have been altered over the years.)

You say the car quickly runs out of fuel.  That could be failure to keep the carburetor supplied - is the fuel shut-off at the vacuum tank open?

What (if anything) do you do to get the car started again (like prime the vacuum tank, etc)? 

If the pump works, and the vacuum tank was properly restored, there could still be trouble caused by vacuum leaks between pump and vacuum tank, as well as any leaks in the line from the gas tank to the vacuum pump.  Make sure that all of your fittings seal properly.

Just some thoughts that might help.

Best regards,

Chris

[CalCadGuy]

Chris, thanks for reaching out. I purchased the car about six months ago and have been uncovering alterations as I go. when I purchased the car, the previous owner had removed the vacuum tank and was getting it rebuilt. In the meantime, he put in a fuel pump and connected that directly to the carb. The car ran well, but eventually began to flood. In the meantime, I got the original vacuum tank back from restoration and had the carb rebuilt. I installed the new carb, restored vacuum tank and connected to the vacuum pump and that is when the problems I mentioned began. I never removed the vacuum pump durning this process.

Fast foward to this afternoon. I got home and decided to removed the vacuum pump for the manifold. When I did so, I noticed that there were absolutely no components internally. I looked at the service manual and it has a cross section that kind of describes the internal components, although quite vaguely. I am convinced that this is the source of my problems. Now I have no clue what to do next. Is it possible to locate another pump? Any help would be much appreciated. Marc

[Johan Boltendal #158]

The pump is not needed to have a functioning petrol supply, engine vacuum is enough,   block the line to the pump and if the tank is restored as it should, the system will work fine . Johan   Good idea to replace or restore the pump, might be needed for the wipers but not for the Stewart .

[CalCadGuy]

I confused. If I block the line from the pump on top of the manifold, where does the vacuum tank get its vacuum? It only has the one line running down to the pump on top of the manifold.

[CalCadGuy]

The way my car is currently set up is that the line running off the manifold goes directly to the windshield wipers and the only source of vacuum for the vacuum pump appears to be a line directly from it to the vacuum pump on top of the crank case. I looked in the shop manual an that appears to be how the 355 was set up. it shows a much more complex set up for the 353 and lasalle. Thoughts?

[Chris Cummings]

Early 1931 V-8 Cadillacs (like the 1930 353's) used manifold and vacuum pump vacuum for the fuel system.  There was a check valve in the manifold line for when manifold vacuum was non-existent (e.g., when driving downhill).  In later 1931 V-8 Cadillacs, the vacuum tank was entirely dependent upon the vacuum pump. (Shop Manual, pg. 79).  Sounds like you have a later 1931, if the manifold line goes straight to the wipers.

The vacuum pump has a little piston, the connecting rod of which fits onto an eccentric at the rear end of the camshaft. (Shop Manual, pg. 84, lower right-hand corner).  If you're missing the piston, that's a problem.  My opinion is that you should try to find a good vacuum pump or restore your own.  In the meantime you can connect the vacuum tank to the manifold, understanding that the vacuum tank will only fill while the manifold has vacuum, and that you have no check valve to keep vacuum in the vacuum tank when the manifold pressure is neutral or positive.  Or you can reconnect the electric pump and maybe install some kind of regulator valve so it doesn't overwhelm the carburetor needle valve and flood your engine (most electric pumps put out more pressure than a gravity-fed carb is designed for).

I hope that helps.

Best regards,

Chris

[CalCadGuy]

Thanks Chris. Would you recommend installing installing a check valve and then running the line to the vacuum tank? My vacuum pump is just a shell, has no internal components what so ever. It has been gutted.

[Johan Boltendal #158]

Hi please find a fitted vacuum line system on a late 353  should be about the same on your. Allow me to be strongly against the electrical pump set up, a recipe for disaster as I see it.

[Chris Cummings]

Marc,

Your vacuum pump is missing only the piston and its connecting rod.  The pump consists of the piston assembly and the housing (which you have). 

In Johan's photo, the vacuum line is the one that runs parallel to the (horizontal) spark advance rod (the line with a sinuous sine-wave curve is the fuel line).  You can see the check valve where the vacuum line meets the manifold.  I'm betting your car doesn't have that check valve.

If you ran your vacuum line from the vacuum tank to the manifold with a check valve, that should work.

I agree with Johan about electrical pumps on these cars.  The pump can easily overwhelm the carburetor and spill gasoline on hot engine parts.  I think the best way to go is to get your vacuum pump working.  That's the way the factory decided the '31 V-8 ought to run (the next year they went to a mechanical fuel pump and made all of this stuff moot).

You could see if Pete Sanders, Wayne Ellsworth, or Dick Shappy has a vacuum pump for a '31 V-8.  All three have lots of early 1930's Cadillac parts and they are reputable gentlemen.  If you are a CLC member, they are all in the Directory.

If you haven't already, you should get a copy of the Shop Manual (copies are frequently listed on eBay).   

Best regards,

Chris

[Chris Cummings]

P.S. - How about a picture (or two) of your car?

Chris

[fishnjim]

Caution: Don't just connect the vacuum tank direct to the manifold without some type of check like the later brake boosters.
That makes it possible to suck gas into the manifold when the tank fills and dangerous.
 

[Chris Cummings]

The float in the vacuum tank trips a shut-off at the vacuum inlet when the fuel rises sufficiently, and at the same time the float opens an air vent to let the accumulated fuel leave through the fuel line to the carburetor.  Sucking fuel into the manifold is not an issue.

The check valve that Cadillac installed on the 1930 and early 1931 V-8 engines was intended to retain vacuum in the system when the manifold pressure was zero or even positive.  A check valve in the other direction would be counterproductive.

Chris

[CalCadGuy]

Thanks for all the information Chirs Johan and Jim. I have a good sense of were I need to go. How difficult is the install on a Vacuum Pump. I believe I have found one. Here is a picture of my car for those interested.

[Chris Cummings]

That's a magnificent car, Marc.  Congratulations!

The vacuum pump should be a very simple install.  I would cut a gasket (cork or fiber) if you don't already have an intact one, and fit it over the mounting studs on the crankcase.  Then I would take the piston out of the housing, insert the connecting rod end into the hole in the top of the crankcase, and engage the loop on the end of the connecting rod (the bearing) with the eccentric journal on the end of the camshaft.  That should be pretty easy to do by feel.  Once the piston is attached to the camshaft, I'd lightly lubricate the piston head and insert it back into the housing as I moved the housing into position, engaging its mounting flange with the studs protruding from the top of the crankcase.  Attach the nuts (and lock washers, if applicable - I haven't handled one of these in decades) and tighten them (I'd tighten them just enough to flatten the lock washers).  Then attach your vacuum line and you should be good to go.

[Chris Cummings]

Marc,

Go to this link:

https://www.gmheritagecenter.com/docs/gm-heritage-archive/vehicle-information-kits/Cadillac/1931_Cadillac_V8_VVI.pdf

on the GM Heritage Center web site for your 1931 V-8 owner's manual, the Preliminary Service Information that Cadillac sent to the dealers when the 1931 V-8s first came out, and some other informational goodies.

Best regards,

Chris

[CalCadGuy]

Thanks Chris, Marc

[houseboats1]

Hello Marc
I can send you some pictures of what the vacuum piping should look like if you like. Also buy a cheap vacuum gauge, screw a fitting to the top of your vac tank and check the vacuum. Also if you have an electric fuel pump you can get an adjustable valve that is attached to it or buy one separately , it reduces the pressure down so you don't get flooding. The vac system can be a real cow if its not just right. I have put 12v Led turn lights on my 31 and still have a 6v system I should share this on the forum.
Let me know if you need the pictures.

[Chris Cummings]

Mark,

I would be interested in how you installed the turn lights you mentioned.

Thanks!

Chris Cummings

[CalCadGuy]

Mark, I would love to see some pictures of the vacuum pipping. That would be really helpful. Marc