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Old 08-01-2010, 12:09 AM
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Fuel disappearing from fuel line at carb

The car is a 57' caddy with the original 365" that I picked up last night.
The fuel line has a dangerous glass fuel filter near the carb so I can see whats happening. The engine wont start without a shot of starting fluid first and thats probably because there isnt any fuel at the carb which is an edelbrock that the previous owner installed. But there should still be some in the float bowl?
After the engine is shut off, you can see the fuel through the clear filter is draining, in turn leaving the line at the carb after the pump empty. The fuel is not seeping through the line or leaking at any connections.
Leaking fuel pump diaphram?

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Old 08-01-2010, 01:13 AM
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The carb has the needle and seat to keep fuel in the carb bowl, but if the level becomes low and the fuel pump check valve is leaking internally, it can and will allow the fuel to drain out of the fuel line and even the carb bowl, to the level of the fuel line entrance.

There still should be enough fuel in the accelerator pump well to provide a start up shot or two of fuel. This could evaporate too, I suppose- if the engine heat was excessive enough to do so- but I wouldn't suspect it to do that under normal conditions.

Bottom line is the fuel pump check may be the problem.
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Old 08-01-2010, 05:53 AM
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That seems to be not unusual with an Edelbrock Performer carb. I've had a total of 4 of them on different engines and they all seem to have the fuel 'disappear'. Interestingly, overnight is/was not a problem as all have started the next morning fine - a week later, it's a grind and grind some more. The carbs have all been brand new as were the fuel pumps in 3 of the four. The only explanation that I've been given (by Edelbrock) was that I needed a non-metallic insulator to keep the engine heat from boiling the fuel out. Obviously that was wrong per the above plus the all had an insulator. An electric fuel pump replaced the mechanical on one engine and did work best as it refilled the float bowl in a couple of seconds.

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Old 08-01-2010, 07:47 AM
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Quote:
Originally Posted by cobalt327
The carb has the needle and seat to keep fuel in the carb bowl, but if the level becomes low and the fuel pump check valve is leaking internally, it can and will allow the fuel to drain out of the fuel line and even the carb bowl, to the level of the fuel line entrance.

There still should be enough fuel in the accelerator pump well to provide a start up shot or two of fuel. This could evaporate too, I suppose- if the engine heat was excessive enough to do so- but I wouldn't suspect it to do that under normal conditions.

Bottom line is the fuel pump check may be the problem.
This is most likely the issue or at least part of it. You may have 2 issues the pump check valve and the famous Edlebrock leak. You also could be boiling the fuel out of the carburetor while parked. I would address the fuel pump first. You can prove that it is draing back by pinching the rubber line , if it has one, somewhere before the glass filter.

Please stop spraying starting fluid into the engine to start it. It is dangerous for you and probably the worst thing for your engine. Use a little gas to start it. If you crank it it should be filling the carb and filter. If this is not happening it is almost a sure sign your pump is bad.
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Old 08-01-2010, 08:00 AM
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Quote:
Originally Posted by Irelands child
That seems to be not unusual with an Edelbrock Performer carb.
Just replaced the Edelbrock 500 on my Stude because of that. I put an R-8007 390cfm Holley on it, it can sit for weeks at a time now and it pops right off.
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Old 08-01-2010, 09:15 AM
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Quote:
Originally Posted by Hippie
Just replaced the Edelbrock 500 on my Stude because of that. I put an R-8007 390cfm Holley on it, it can sit for weeks at a time now and it pops right off.
I wonder if that's one of the reasons that so many companies, including Edelbrock, are selling 'remanufactured' Performer carbs

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Old 08-01-2010, 09:28 AM
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the holley 390 is the perfect match for a sbc street engine. fuel is most likely evaporating . it can not drain back from the bowl. a 1 in phenolic spacer will help.
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Old 08-01-2010, 05:26 PM
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Quote:
Originally Posted by T-bucket23
I would address the fuel pump first. You can prove that it is draing back by pinching the rubber line , if it has one, somewhere before the glass filter. Use a little gas to start it. If you crank it it should be filling the carb and filter. If this is not happening it is almost a sure sign your pump is bad.
I will check more of the pump when I get off work in the morning. But how would pinching the fuel line before the filter verify the pump? If the fuel in the carb was evaporating, would'nt the fuel stay in that part of the fuel line and filter since it sits lower than the carb fuel inlet? It seems that the fuel is draining from the fuel line by watching it disappear in the glass filter which also sits below the carb fuel inlet.
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Old 08-02-2010, 02:18 AM
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I just had did a post on this, then I thought back for a second and had another thought come to mind. Remove the carb and look at the intake`s carb pad. Are there 2 small holes in the intake that are connected to each other with a trench? If so, these are the heat riser passage holes that are plumbed directly to the exhaust heat riser passages. The set up these engines used was, gasket, steel plate, gasket. The steel plate and gaskets together would seal off the trench between the holes causing it to stay in the trench. It has 2 jobs, one is prevent carb icing in the winter time, the second is to help cold starts since the heat would heat the incoming fuel charge, helping it burn easier. My nephew`s 69 Caddy 472 had a Quadrajet on it, but the intake had the 2 holes connected to a trench, he used a junk adapter plate and a holley carb and never could get it to run correctly, I showed him the 2 holes and told them how it worked. He got a Quadrajet for it and the correct carb base gasket which solved the problem. I`m not sure if they did it this same way in 1957, but it`s worth a look. If these holes are present and open, the engine is pulling in exhaust gasses, which can`t be burned twice, this will cause it to run rough and be low on power. the second thing it causes is the carb will get very hot and boil the fuel out of the carb once the engine is shut down. What happens after shut down? heat rises and collects under the carb. As for fuel draining back after shut down, yank the oil dipstick out and smell it, if it smells like gas the fuel pump is no good.
If the fuel pump has a return line, crimp it closed with a pair of vice grips, let it idle a few minutes, shut it down and see if it drains back. If it does then I would replace it. I`m not sure if the fuel pump or the fuel tank has anti reversal check valves or not, but it draining back would suggest it`s stuck open.
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Old 08-02-2010, 03:59 AM
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What DV says is true but Edelbrock "AFB" style Performers are also becoming notorious for this. I thought mine was heat related at first but it even did it in the dead of Midwest Winters. I'd get it started and never even run the engine long enough to get it more than warm to the touch and a day later the carb would be dry. Put the Holley on with the same fuel pump and the problem is gone. If Studebaker had ever made a spreadbore intake it would have received a Q-Jet instead.....
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Old 08-03-2010, 10:05 PM
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Well it looks like some fuel is dissapearing from the carb bowl, I verified it is definitely leaking internally back through the fuel pump. I think I will rebuild both of them this winter. Thanks!
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Old 08-03-2010, 10:52 PM
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Another data point.

I have accepted that my edelbrock performer will not hold fuel in bowl long term and it will not hold pressure between edelbrock pump and carb very long after shut down.

I spent some time with edelbrock fuel pumps, spacers, rebuilds, etc.

I still like my edelbrock carb because it won't leak fuel externally like some other carbs and it is easy to rebuild and tune and my car runs good. My complaint is I must crank awhile if I let car sit a few weeks.
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Old 08-04-2010, 07:24 AM
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One point I`d like to mention. On Holley, demon and edelbrock carbs, the point of fuel entry is higher than the float level so fuel can`t drain out via the fuel line unless I`m missing something here. A Quadrajets seat is above the fuel level unless it`s using a "windowed" seat assembly.
Fuel can`t travel up so there`s no way that I can see it would be draining out of the fuel line so the fuel in the bowl is either evaporating or leaking out of the bowl itself. If the heat riser passages I mentioned aren`t block off properly when the vehicle is shut down heat soaks under the carb. take the car down the road about 10 miles. Remove the air cleaner and touch the carb, if it`s so hot you can`t leave your finger on it you can bet the heat riser holes are open and if the carb is getting that hot there`s no doubt the fuel is evaporating.
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Old 08-04-2010, 08:43 AM
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I've often wondered why my truck takes longer to crank and fire up the longer it sits. I too have a Performer carb. Sitting for a week or less is okay. 2 weeks or longer and it's quite a bit of cranking.
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Old 08-04-2010, 10:11 AM
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Quote:
Originally Posted by K and K
I will check more of the pump when I get off work in the morning. But how would pinching the fuel line before the filter verify the pump? If the fuel in the carb was evaporating, would'nt the fuel stay in that part of the fuel line and filter since it sits lower than the carb fuel inlet? It seems that the fuel is draining from the fuel line by watching it disappear in the glass filter which also sits below the carb fuel inlet.
If the glass filter stays full then you know it wsa draining back. The fuel dissipating from the carb is a different issue. As mentioned above, it is a common Edlebrock issue to leak fuel internally, could also be boiling out.
Fix the pump and go from there
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