COLD START PROBLEMS 1978 Caddy

[TJ Hopland]

Its got to be Gnomes then.   They need gas for their little cars. 

I suppose one of the valves in the fuel pump could be weak but then you would think it would have been a more common issue.  Maybe the new pump will help.

[R Schroeder]

Ha - I suppose.
We will see if a new pump makes any difference. Should be in next week sometime. Couldnt find anything in the repair manual that showed the inside of the pump.
Whatever it does , I'll be driving it. Leak down or not.
Roy

[TJ Hopland]

The pump basically has 2 check valves on it.   They are not there intentionally as back flow preventers, they are how the pump works.   The pump is just a diaphragm that moves up and down.   On the down stroke the out carb side valve gets sucked closed and the tank side opens so fuel gets drawn in.   On the up stroke the pressure closes the tank side and the carb side gets pushed open by the fuel that is now flowing out.   The pressure is regulated by the coupling between the pump arm and the diaphragm.   Too much pressure and the coupling just collapses so the diaphragm does not move as far therefore not generating as much pressure.   Pretty simple and reliable design that pumps air as well as it pumps liquid so it primes easily and does not have a problem with chunks as long as they go through the valves.       

[R Schroeder]

I knew it had check valves. It has two lines coming from the tank, so I think some gas is returned to the tank. Maybe the one that returns has no way to stop the flow, like the side with the check valves in it. I think I'm starting to babble here.
I'm I making any sense ?

[Wayne Womble 12210]

The mid 70s Corvette has a check valve in the fuel filter.  Thats the longer paper type filter in the Rochesters.  Not sure about yours though.

[R Schroeder]

Up at the carb Wayne is a spring that just holds the filter in place. There is about an inch and a half long filter in the carb.
I had a 77 Vett, but it was a long time ago. Back in 1983. Cant remember the set up on there.

[Wayne Womble 12210]

Same set up.  You will notice there is a little check valve inside the filter.

[R Schroeder]

Well, sure enough , there it is. I never knew that there was one in there. Must have looked right at this picture a few dozen times. Never looked at the filter part.  Learn something new everyday. 50 years of working on cars ,and you still pick up something new. I'll have to check that out today.
It still will get a new fuel pump. Then I know all is new on the system.
Thanks for the info. Maybe with the help of all you guys , I'll get this solved.
Thanks
Roy

[R Schroeder]

Hit another dead end.
It appears that Cadillac designed it that way, but it must have changed over the years. As you can see my carb has a flat bottom in the holder, not the taper shown , and just the gasket on the end of the filter. Maybe the check valve gave them a problem.  As far as I'm concerned it made another problem.  I cant remember ever seeing one with a check valve in it. Did a lot of quads too.
It sure would have been nice to find it in there. As you can see the car was bone dry when I took it apart. Car sat for the last two days.
I wonder if there is a in-line check valve one could install.
Back to the drawing board.
Maybe the fuel pump will stop the bleed back. Not real hopeful.

[R Schroeder]

Never mind about the flat bottom in the holder. I looked at the drawing again, and it is flat. The filter is what has the taper in it at the opening.
Anyway I checked in the book as to the filter number and it is AC - GF441.
I don't know if I got a generic one , or its missing the check valve, or they just don't make them anymore.
I'll have to do some checking on it.
Roy

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Been checking on this filter. Again I find the repair manual is wrong . The GF441 doesnt have the check valve. The GF471 does have it.
So, I just have to order the GF471 and my problem should be solved.
Roy


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Found that all the auto parts stores around here carry the part.

Back on track again. Man what a trip.

[R Schroeder]

Went and got the filter with the check valve in it, and installed it. Test will be tomorrow.

[TJ Hopland]

Fingers crossed.            It couldn't be that simple could it?   I will have to go look at some of the Qj's I have laying around so see how many have the valve.

[R Schroeder]

T.J. - The filter with check valve made no difference. Float was down this morning. Last hope is the fuel pump.
I did notice yesterday when I was putting filter in that the gas was out of there right away after I shut it down.
Took fuel line off within minutes of shutting it down, and it was drained out.
After starting the car, the float was up.
This is crazy.....hey ?

[R Schroeder]

Just picked up the new fuel pump. You can blow through the carb connection line to the fuel tank return line. The gas inlet line is blocked by the pump valves, so I'm not all excited that the line wont bleed out again.
Pretty much open from the carb to the tank through the return line.

[Wayne Womble 12210]

If all else fails, start the car and fill the bowls, then quickly and carefully remove the carb and set it on the bench.   Watch it and see where the fuel is going.  I dont think it will evaporate that quickly, but you need to determine once and for all if its the carb or the lines that are the culprit. Or if its a combination of heat and evaporation.   

It might help to set out a few traps for the gremlins. 

[R Schroeder]

This is starting to become a real mystery. I feel its the line that is causing the problem.
Well, check valve in the carb filter didn't help much either. Maybe I  can put some gasket sealer on the end of it to make sure its sealing on the face of the holder. They have some gas resistant ones out there.
I don't know. It has been one hell of a problem. Everytime you think you have the answer it pulls you down again.
I just cant believe its running out of the bottom of the bowl, because there is always some gas in there . I can pump it 3 to 4 times before its dry.
If it had a leak it should all leak out.

[R Schroeder]

Another bit of luck. Fuel pump I bought isnt working. Arm moves up and down, but pump inside isnt moving.
I'm about ready to buy a YUGO......................ha

[TJ Hopland]

Just for a 'control' test perhaps set a small open container with a similar amount of fuel somewhere to see how much disappears on its own.   Maybe that is just what happens to our modern fuels when left in the open?   

Just for fun I looked on ebay for Yugos.  None for sale.  Like many car related things on that site 90% spammers, full page of ads for the identical car cover and then another page for seat covers.   I have actually not bought items from sellers that do that because it bugs me so much.   I look for a seller that only has it posted one time. 

[R Schroeder]

Well, I'm going to be playing with it for the next week. Thats for sure. I bought a NOS vacuum advance off of some guy up in Mn.
Seems there are 4 different ones for my 78 . Found the one I need on Ebay yesterday.
So, with that and waiting for another fuel pump, more time will pass.
Maybe I'll go and work on my truck for awhile.....ha.  Got heater hoses and radiator hoses to replace on that animal.

I will try the control test for kicks, but I think it is just running back down the line.

[dadscad]

As TJ stated, it could very well be fuel evaporation. The fuel in my 63's carter seems to disappear after a couple of days of sitting. If the car is driven daily, no problem, it starts right up cold after sitting all night. Let it sit 2 or more days and I have to crank it a little to fill the fuel system back up.

Do you have a Mighty Vac? Now that you have the fuel pump off and the line disconnected there, try pulling a very light vacuum on the fuel line to the carburetor. If you draw fuel out of the carburetor you will know there is a leak in the needle and seat area.

David