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Strange fuel issue
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poly
Posted 2022-12-18 5:40 AM (#626410)
Subject: Strange fuel issue



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Location: Melbourne, Australia		I'm having an ongoing issue with fuel delivery / pressure and I need some help to sort it out...

About 18 months ago I fitted an Edelbrock AVS 650 carb to my 440. It runs standard fuel lines with a clear plastic fuel filter fitted horizontally between the pump and carb. There is a small pressure gauge on the hard line. Everything ran fine , although I was wondering why the filter never seemed to have much fuel in it or much flow....but, what the heck, it ran.

Just recently, the car started to stumble and even backfire after driving for a while.
Now I noticed that the pressure was fluctuating so I swapped the mechanical pump. All good for a bit then same again.... I decide to try an electric pump. This has about 4.5 PSI and a good flow.

When I started the car, the fuel filter filled up about 80%....Great! I've solved the problem......Go out driving and all is well, until it starts acting up again. Pull over and see the filter is basically empty, and there is only the odd squirt of fuel going into the filter

To date: I've tried putting the filter in various positions / locations along the line, removing the filter, reset the floats, installed higher flow needle and seats, blown out the lines, cleaned out the tank and replaced the pickup screen, everything seems to work initially but ends up the same..
I've tried bypassing the tank, even removed the line at the carb and ran into a bucket to verify flow .

I then though maybe some sort of vapour lock... my engine bay gets very hot ... so i have tried rerouting the fuel line and wrapping it in insulation.
After a hard drive today I think it was a bit better BUT I still had some hesitation and backfire AND when I pulled into the garage the pressure was showing almost zero with an empty filter and hardly any flow....very odd.


So a few questions....

What could have changed after all this time to start giving me grief?

As the electric pump is low pressure and deadheaded like the original, why don't I see fuel flow into the filter? Shouldn't it always be mostly full?
When the pressure drops to nearly zero, because I assume the needles are open, shouldn't the pump allow flow through the filter?
Is this a heat problem? But why now?

Any thoughts on these or clues as to my next move are most welcome...

Thanks, Frank
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wizard
Posted 2022-12-18 6:15 AM (#626411 - in reply to #626410)
Subject: Re: Strange fuel issue



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Location: Southern Sweden - Sturkö island		It might be that fuel hose has collapsed due to the ethanol mixed in the gasoline. Try checking all the fuel hoses.
It might be a small rust hole in the hard line, high up, not allowing the gasoline to leak, but air can be sucked in.
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Rebels-59
Posted 2022-12-18 10:16 AM (#626412 - in reply to #626410)
Subject: Re: Strange fuel issue



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Location: .Norfolk..Mafia.. ,England UK		Also check to see if you have a Vented fuel Cap,, If you drive the car with fuel cap removed see if it makes a difference ,, As this could cause Vaper lock to the Filter and Carb
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Powerflite
Posted 2022-12-18 11:10 AM (#626413 - in reply to #626410)
Subject: Re: Strange fuel issue



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Location: So. Cal		If you don't have a collapsed hose, put a pressure gauge inline and check it once it starts to give you trouble. If the pressure looks good, you know it has nothing to do with your fuel delivery. I've had issues with a partially blocked line before, but it just causes the car to lose power & shut off under load. It doesn't cause a backfire. Backfires are commonly caused by valve issues. So I recommend doing a leak down test to check them - preferably after the car is warmed up and starts to give you issues.

I had an annoying backfire issue with the hemi in my Savoy that only happened when it was under a lot of load. It gradually got worse & worse to the point that I couldn't really drive it without issues. I assumed it was caused by a loose timing chain or some fuel delivery problem, but that wasn't it. It needed a valve job and better springs installed. After that, no issues.
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Powerflite
Posted 2022-12-18 11:12 AM (#626414 - in reply to #626410)
Subject: Re: Strange fuel issue



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Location: So. Cal		Oh, and by the way, the level of fuel you see in those see-through filters usually have nothing to do with your fuel delivery. On all my daily driver cars with those on them, they look mostly empty while running.
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Shep
Posted 2022-12-18 5:43 PM (#626425 - in reply to #626414)
Subject: Re: Strange fuel issue



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Location: Chestertown, NY ( near Lake George)		Not sure here it but was a known issue on GM cars back in the day, the fuel line in the tank had a sock type filter that would collapse closed after hard driving periods.
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poly
Posted 2022-12-19 3:40 AM (#626435 - in reply to #626410)
Subject: Re: Strange fuel issue



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Posts: 161
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Location: Melbourne, Australia		An update: I've replaced all the rubber lines so I know they are ok. The steel lines are solid. I decided to go back over the carb and discovered that the phenolic spacer under the carb was warped. I have ordered a new one so we'll see how that works when I get it.....
Thanks for the answers provided so far.......
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poly
Posted 2022-12-20 1:46 AM (#626460 - in reply to #626410)
Subject: RE: Strange fuel issue



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Posts: 161
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Location: Melbourne, Australia		Just wondering which spacer is the correct one to use on this manifold, which I believe is a dual plane?



(20221220_173702.jpg)



(Screenshot_20221220-173816_Samsung Internet.jpg)



(Screenshot_20221220-173739_Samsung Internet.jpg)



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Attachments 20221220_173702.jpg (124KB - 80 downloads)
Attachments Screenshot_20221220-173816_Samsung Internet.jpg (45KB - 81 downloads)
Attachments Screenshot_20221220-173739_Samsung Internet.jpg (48KB - 96 downloads)
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Chrome58
Posted 2022-12-20 2:52 AM (#626461 - in reply to #626410)
Subject: Re: Strange fuel issue



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Location: Belgium, 40 miles south of Brussels		No, I believe it's another adapter, made by Trans-Dapt.

I used the Trans-Dapt 2064 to adapt an Edelbrock carb to my 4-bbl poly intake: https://www.summitracing.com/parts/trd-2064
It was recommended to me by Gary Pavlovich.

Edited by Chrome58 2022-12-20 2:58 AM
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poly
Posted 2022-12-20 4:49 AM (#626462 - in reply to #626461)
Subject: Re: Strange fuel issue



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Posts: 161
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Location: Melbourne, Australia		This is on a 440 not a poly...
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poly
Posted 2022-12-21 1:53 AM (#626478 - in reply to #626462)
Subject: Re: Strange fuel issue



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Posts: 161
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Location: Melbourne, Australia		So I got this today.....it's a heat insulator gasket. Is this the correct one to use on a dual plane manifold with an edelbrock AVS?
Do I need to use a paper gasket either side of it to seal properly?



(20221221_174709.jpg)



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Attachments 20221221_174709.jpg (117KB - 84 downloads)
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poly
Posted 2022-12-30 4:18 PM (#626643 - in reply to #626478)
Subject: Re: Strange fuel issue



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Posts: 161
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Location: Melbourne, Australia		So here's an update...
I fitted the carb with the rubber insulator as per Edelbrock website directions. Started car and sprayed around base, was sucking air under choke side. Removed carb , used paper gaskets either side of insulator, ran car with same result.
Removed everything again and used gasket sealer this time , ran car and still had a leak!!!! The manifold is flat and so is the carb...
I did try driving it and I think it has improved but this is nuts....how do I seal it? Perhaps the rubber like material is porous?
I might look into that next....

Thanks to those who read / responded so far.......Happy New Year to all, bring on a better year !
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wizard
Posted 2022-12-31 5:12 AM (#626653 - in reply to #626410)
Subject: Re: Strange fuel issue



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Location: Southern Sweden - Sturkö island		The Edelbrock carburators are in fact a Carter, made with sometimes lesser quality.
First of all, check with a large sheet of crocus cloth on a very falt surface, carefully grind the base of the carburator and check if the base is true.
Secondly, check if the leak comes from the choke housing - there should be a small evacuation hole for the choke - this might leak too much.
Thirdly, check the carburator itself for casting errors - not uncommon with the Edelbrocks
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58coupe
Posted 2022-12-31 2:48 PM (#626663 - in reply to #626410)
Subject: Re: Strange fuel issue



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Location: Alaska		another area to check especially on used carbs is the throttle shafts. The shaft wears into the carb base and will eventually cause a vacumn leak that can cause a rough idle that is hard to adjust.
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Shep
Posted 2022-12-31 3:30 PM (#626664 - in reply to #626663)
Subject: Re: Strange fuel issue



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Location: Chestertown, NY ( near Lake George)		Loose throttle shafts on the Magnetti-Marelli castings were an issue on new Edelbrocks, check for shaft play.

Edited by Shep 2022-12-31 3:31 PM
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poly
Posted 2023-03-02 5:47 PM (#627995 - in reply to #626410)
Subject: Re: Strange fuel issue



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Posts: 161
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Location: Melbourne, Australia		Ok, it's been a while but I think I've got it sorted. The carb was pulled and given to a reputable shop to look at. They said that the play in the shaft was totally normal and wasn't the cause of my problems.
A compression test gave me 185-195 lbs. I found two spark plug boots had started to break up so replaced those. Also new plugs fitted. The engine took some adjustments of idle mixtures and timing , in conjunction with a vac gauge , to get it to run nicely. Also some fresh 98 octane fuel in the tank. Took a few test drives with good results....power with no stumbles or pinging. I now believe that my fuel issues, i.e. stumbling, backfire, erratic fuel pressure was a result of a poorly running motor which slowly got to the point of giving up! Just shows that the obvious cause is not always the case.
Thanks to all that responded with helpful ideas....
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