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1956 Cadillac losing prime to the carb

Started by carguyblack, July 20, 2016, 10:16:28 PM

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carguyblack

I've been driving this car for a year now after having the carb restored. Worked great until the last few weeks. The symptom is that there seems to be no fuel to the carb after I try to start it after sitting for a day or two. It will turn over and turn over but not pop at all. Up until now I just needed to kick the pedal a couple times no matter how long it had been that I drove the thing and it would fire right up.
Now it will just about run the battery dead. To remedy, I pour just a touch of raw gas into the carb and it fires right away and continues to run. Without the manual prime it never even sputters.
The has been no work done to disturb anything and all the fuel lines to the carb seem tight with no leaks when running or after it stops. Once running, it never fails and starts right up again when I stop the car for a few hours or more. But overnight or a few days in between running and it is a very different story.
Could this be the fuel pump going bad?
Chuck
Chuck Dykstra

1956 Sedan DeVille
1956 Coupe DeVille (2 sold)
1957 Oldsmobile 98 (sold)
1989 Bonneville SSE

55 cadi

Chuck,

This sounds like my problem i was having.

I replied to another post about it just before yours.

It does sound like air getting into line somewhere now.

Even the tiniest air leak from clamps wont have gas coming out

First cranking the car it is low pump action, but when car is running the pump action is stronger and any tiny air leak wont stop it, only when trying to turn over car for first time.

Maybe check lines again or re tighten them.

Jason
1955 Cadillac sedan series 62
1966 mustang convertible w/pony PAC, now in Sweden
2005 Cadillac deville

carguyblack

I'll do that Jason, and thanks for the reply.
All lines visible are hard pipe around the carb but I'll give them a torque again. I've not looked along the fuel line coming form the tank, but i guess it would not be out of the realm of possibility that it might have sprouted a leak. I don't smell gas in our garage that would indicate a drip somewhere. But, that air thing coming into the line is insidious, though.
Chuck
Chuck Dykstra

1956 Sedan DeVille
1956 Coupe DeVille (2 sold)
1957 Oldsmobile 98 (sold)
1989 Bonneville SSE

TJ Hopland

Since most of the lines are under suction they don't tend to have external leaks till they get really bad.  The mechanical pumps work on strokes / pulses so what happens is when the pump first starts to suck it ends up sucking some air but as the suction increases it may seal up and then draw some fuel along with the air.  Next stroke the process starts again. 

The longer it sits the more air that gets in the lines as the fuel drains back so the less chance you are going to get fuel.   

With a carb the air just gets burped out the bowl vent in the carb so as long as you are still getting enough fuel you won't know its going on till it gets real bad. 
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

carguyblack

interesting, TJ. Thanks for your input. Tonight I re-tightened all the connections and actually put some thread sealer on most of them up near the carb. I also replaced the section of rubber hose from the fuel line that runs up from under the car up to the pump and clamped them with new clamps. Tomorrow or the next couple of days should tell me if I have the old car back that fires right up after one kick down of the pedal or not. Here's hoping!
Chuck
Chuck Dykstra

1956 Sedan DeVille
1956 Coupe DeVille (2 sold)
1957 Oldsmobile 98 (sold)
1989 Bonneville SSE

Jon S

Jon

1958 Cadillac Sedan De Ville
1973 Lincoln Continental Coupe
1981 Corvette
2004 Mustang GT

carguyblack

Still no luck. After replacing the brass connections, rubber hoses and clamping and tightening all the lines I still have a dry carb after an overnight sit. There is gas in the fuel filter sight and there are no juicy connections like before. I also turned the nut off the top of the fuel pump and there was gas in there. But pumping the carb and looking down the throat there is no accelerator pump squirts to get the engine to fire.
I don't think I have a clogged fuel line seeing the fuel I see, but could I have a carb problem? My carb is a Carter and I wonder if there is some sort of check valve in the fuel chambers that is stuck open and drains them out in between uses? I have not checked any lines back at the tank itself but I thought all those were hard lines. What would cause the carb gas to disappear after less than 12 hours?
Again, the beast runs flawlessly with no hesitation after dumping a manual prime down the carb but to get it to fire on its own is impossible.
What would you guys do next?
Chuck
Chuck Dykstra

1956 Sedan DeVille
1956 Coupe DeVille (2 sold)
1957 Oldsmobile 98 (sold)
1989 Bonneville SSE

Jon S

My symptoms were very similar. Turned out to be a clogged fuel line.
Jon

1958 Cadillac Sedan De Ville
1973 Lincoln Continental Coupe
1981 Corvette
2004 Mustang GT

chstitans42

I would consider changing out the accelerator pump. Same issue I had on a 64 Mercury. Now it fires up with two pushes of the pedal and one turn of the key.

carguyblack

OK, my next move will be to clean all the screens (carb & fuel pump) and blow the line from front to the tank. Is there any risk in damaging an in-tank screen inside the gas tank when I do that?
Thinking ahead a few steps, if I were to need to clean my gas tank out, can this be done on the car or would it need to be removed from the car?
Chuck Dykstra

1956 Sedan DeVille
1956 Coupe DeVille (2 sold)
1957 Oldsmobile 98 (sold)
1989 Bonneville SSE

TJ Hopland

Is this a AFB?    I am kinda remembering there was something on the bottom of those that could leak, it was some sort of cap that had to do with the accelerator pump maybe?
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Jon S

Quote from: TJ Hopland on July 24, 2016, 02:15:13 PM
Is this a AFB?    I am kinda remembering there was something on the bottom of those that could leak, it was some sort of cap that had to do with the accelerator pump maybe?

You're confusing Carter AFB's with a Rochester Quadrajet problem.  His car has either a Carter or a Rochester 4GC.

As to blowing out the fuel line, I just gave mine one gentle spurt of compressed air and all was well.  Could hear bubbling in the tank.  Be gentle with the air.
Jon

1958 Cadillac Sedan De Ville
1973 Lincoln Continental Coupe
1981 Corvette
2004 Mustang GT

Lexi

#12
Chuck how are yeah?  Hope all is well with you. I had the same thing happen to my '56. In my case it turned out to be the so-called "strainer nut" on top of the mechanical fuel pump. That is the large bolt on top. 7/8 inch I think, you can't miss it. When I did volume tests with my pump it was just not putting out. Just for testing I hooked up an electric fuel pump to the inlet side of my mechanical pump and it is then that I noted gas leaking all over the place from the strainer nut. As that is the suction side I did not see gas leaking from it under normal use. The electrical pump put pressure there and then the leak showed.

So I had an air leak there. This reduced the volume of gas reaching the carb. Upon (cranking) attempting to start the engine, the pump did not provide enough suction to pull gas and feed it to the carburetor. I too had to prime my car to start it. Once started it ran fine as the higher rpms when the engine fired overcame the weak fuel delivery issue, but I suspect my car only got enough fuel to keep it running. Once turned off and left to sit, especially overnight, I had to prime it to start the engine. Gas will also normally evaporate through those 2 vent tubes in the throat of the carb. It is not a sealed system like new cars. So that contributed to the problem. I suppose I could of removed those bowl nuts to see how much fuel was actually reaching my carb bowl at any time, but testing showed that in my case it was the fuel pump (sucking in air), as the cause of the problem.

Anyways, in my pump under that strainer nut was a metal washer which no longer sealed properly. Flipping the washer upside down actually worked to seat in better but to be safe I replaced it with a combo metal-viton (transmission) washer from a parts supplier. Worked. For good measure I then wrapped the strainer nut's threads with gas fitters tape (not teflon). Gas flow then doubled and problem solved. Hope this helps. Can provide more info if needed. A vacuum gauge can be used to conduct several tests on your pump to determine its mechanical health. Clay/Lexi

TJ Hopland

Quote from: Jon S on July 24, 2016, 02:18:44 PM
You're confusing Carter AFB's with a Rochester Quadrajet problem.  His car has either a Carter or a Rochester 4GC.

No, I'm not thinking of all the plugs in the Qjets, I know those didn't come out till the mid 60's.  I don't know if the Carter Cad was using in 56 was the AFB or the previous model.   The AFB has a threaded? plug in the bottom of the main body.  I think its got a jet or check ball or something under it.   What ever it was it was really abused and leaking on the last one I tangled with.   I ended up taking into a shop to deal with it because it was so screwed up when I got to it I could not even get it out.   If its not a threaded plug then what is under the plug is threaded.  I didn't spend a lot of time on it so I don't remember the details but it was a 1957 AFB and it was leaking.    I do remember when I called the shop and started describing the problem they said 'oh ya we see that a lot on those and can usually fix it' and they did no extra charge.   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Jon S

Never had any problems with myAFB and I've rebuilt it 4 times over the years.
Jon

1958 Cadillac Sedan De Ville
1973 Lincoln Continental Coupe
1981 Corvette
2004 Mustang GT

TJ Hopland

So being into them that many times you don't remember any sort of plug in the bottom?   Maybe it was a one year only thing I ran into?
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

carguyblack

This morning after running the car yesterday, I took a look over the carb to see if miraculously it had fixed itself. It hadn't and there was no fuel in the accelerator pump to prime the carb. However, I noticed some bubbling in the sight glass of the fuel filter which indicates to me that I still have a suction leak in the lines somewhere.
I'm now wondering if I don't have something wrong with the fuel pump itself. Aside from the bolt on the top of the pump, could the diaphragm itself be leaking around it causing air? I hate to just throw parts at this problem but I'd sure do the pump again if needs be.
Chuck
Chuck Dykstra

1956 Sedan DeVille
1956 Coupe DeVille (2 sold)
1957 Oldsmobile 98 (sold)
1989 Bonneville SSE

Jon S

Quote from: TJ Hopland on July 24, 2016, 10:49:50 PM
So being into them that many times you don't remember any sort of plug in the bottom?   Maybe it was a one year only thing I ran into?

4 rebuilds over 50+ years . . . really don't remember any plug in the bottom.  But then I've rebuilt Holley's, Motorcraft , 4GC's and Quadra-Jets.  Sort of lose track.
Jon

1958 Cadillac Sedan De Ville
1973 Lincoln Continental Coupe
1981 Corvette
2004 Mustang GT

TJ Hopland

So the bubbles happened after you operated the throttle to look for signs of gas coming out the accelerator jets?     What carb is this?     

StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Jon S

Quote from: carguyblack on July 25, 2016, 09:17:14 AM
This morning after running the car yesterday, I took a look over the carb to see if miraculously it had fixed itself. It hadn't and there was no fuel in the accelerator pump to prime the carb. However, I noticed some bubbling in the sight glass of the fuel filter which indicates to me that I still have a suction leak in the lines somewhere.
I'm now wondering if I don't have something wrong with the fuel pump itself. Aside from the bolt on the top of the pump, could the diaphragm itself be leaking around it causing air? I hate to just throw parts at this problem but I'd sure do the pump again if needs be.
Chuck
[/quote

Bubbling in the fuel filter glass is normal after the engine reaches operating temperature - they all do that.
Jon

1958 Cadillac Sedan De Ville
1973 Lincoln Continental Coupe
1981 Corvette
2004 Mustang GT