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Technical Edelbrock loosing fuel

Discussion in 'The Hokey Ass Message Board' started by pull toy, Apr 22, 2021.

  1. pull toy
    Joined: Aug 22, 2013
    Posts: 81

    pull toy
    Member

    I know the discussion about fuel evaporation has been around the block a few times. I have a Edelbrock 1450 on my 454 and I was wondering if anyone has had experience with that carb leaking into the manifold after the engine is turned off. After sitting 24 hours my carb is dry. Besides evaporation can it be leaking or maybe syphoning back. I also run the 6 psi Edelbrock mechanical fuel pump which should have a check valve. Any input appreciated.
     
  2. Rckt98
    Joined: Jun 7, 2005
    Posts: 1,043

    Rckt98
    Member

    There have been several threads about this subject. I'm not sure anyone came up with an answer other than to put a pump in the line to pre prime the carb. I have had the same issue with an Edelbrock carb on my small block and fixed it by using a marine squeeze bulb in the line before the fuel pump.
     
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  3. pull toy
    Joined: Aug 22, 2013
    Posts: 81

    pull toy
    Member

    I have debated adding a low psi electric pump just to prime the carb but there is a real fire danger since my ride is a coe with a enclosed engine compartment, if the pump overrun the carb and a backfire occurred then it would be a total loss. Just got to be a better way.
     
  4. jimmy six
    Joined: Mar 21, 2006
    Posts: 9,443

    jimmy six
    Member

    No carb should syphon fuel from the bowls into the venturi boosters or from anywhere under or over the throttle blades. I would believe evaporation which can be slowed or stopped by and insulator. But if all the fuel is gone in 24 hours you have a serious carburetor problem.
     
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  5. SlamIam
    Joined: Oct 8, 2007
    Posts: 448

    SlamIam
    ALLIANCE MEMBER

    A 1" non-metallic carb spacer fixed mine - starts quickly hot or cold - guess it could also depend on how hot it stays under the hood after shutdown - I have a large engine bay that cools quickly
     
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  6. gene-koning
    Joined: Oct 28, 2016
    Posts: 2,417

    gene-koning
    Member

    I ran low pressure electric pumps on carbed motors for many years (and lots of miles) and never had one overflow a carb.

    I don't buy into the syphon back theory, if the carb float is working, it should seal the back flow. The fuel could drain back into the tank from the carb inlet, but what is in the carb float bowl should stay there.

    Fuel boiling out of the carb after shutdown can be a problem, I've seen it in real life before. I've also seen the fuel drain out of the carb and down into the intake (and even outside of the intake) as well. Does the oil smell like gas?

    The carb could also be loosing fuel through evaporation, but it doing so in a 24 hour time is pretty short unless the temperature is really warm where the motor is located, or unless the fuel is a winter grade fuel that can evaporate pretty fast when it gets into the 60s.

    Add the low pressure electric fuel pump. Put it on a time delay so it only runs 30 seconds if you would feel better. 30 seconds will fill the float bowl enough to start the motor. Gene
     
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  7. ProtoTypeDesignFlauz
    Joined: Jul 29, 2007
    Posts: 1,116

    ProtoTypeDesignFlauz
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    Evaporation is stealing all our precious fuel, then we have to purchase more. The petroleum companies got a gig going on with this alcohol blended product that they refer to as gasoline. Back in the old days .... gasoline smelled like gasoline should. Gasoline now smells nasty, compared to the way it did, 20 or 30 years ago.
     
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  8. Mr48chev
    Joined: Dec 28, 2007
    Posts: 29,539

    Mr48chev
    ALLIANCE MEMBER

    I've seen/had gas percolate with a hot engine after shut down but as Jimmy six said they don't "siphon" the gas out into the intake With the idle air bleeds working that is pretty well impossible.
    For that to happen the fuel outlet into the venturi would have to be below the level of the float bowl with no air inlets in the system. The idle air bleed lets air in and prevents siphoning just as a hole in your siphon hose prevents siphoning.
    On the COE I am going with the concept that the engine compartment is closed up enough that it retains engine heat far longer than a lot of engine compartments do. That is letting the gas boil in the carb. Throw in today's crappy gas and the boiling point is a lot lower.

    idle ckt.JPG
     
  9. squirrel
    Joined: Sep 23, 2004
    Posts: 49,257

    squirrel
    Member

    The Edelbrock carb (like the AFB it's a copy of) has two huge float bowls, that take a long time to refill after the fuel evaporates.

    Yes, it's just evaporating.

    Get a Qjet, they have a tiny float bowl that refills quickly.
     
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  10. xlr8
    Joined: Jun 26, 2006
    Posts: 698

    xlr8
    Member
    from Idaho

    This is pretty much a trait of Edlebrocks, we have 3 of them, some lose all the gas in one day, others it takes 2 or 3 days. There is one advantage to the gas nowadays that evaporates quickly, 10 or 15 years ago the crap gas we had back then would congeal into a sticky mess in engines that weren't run for a few months, now it just evaporates almost immediately and plugged up jets, etc. are not near the issue that they used to be.
     
  11. Lloyd's paint & glass
    Joined: Nov 16, 2019
    Posts: 4,827

    Lloyd's paint & glass
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    What he said ^^^^ I tend to use edelbrock carbs on just about everything i build. Usually pick them up at the local swap meets for $50 or less, and the rebuild kits are on the shelf at o'Reilly's, so it's a cheap way to go. I've had many that you could look down the venturi's after shutting it down and watch gas dripping out of the boosters. I found an article online from edelbrock about the air bleeds that needed to be cleaned to prevent this. Hasn't been a problem since. Good use for them old torch tip cleaners. I've also heard about the spacer under the carb to prevent boiling since there isn't an air gap under the fuel bowls like a Holley.
     
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  12. pull toy
    Joined: Aug 22, 2013
    Posts: 81

    pull toy
    Member

    Your comment about my coe holding heat in the engine compartment longer than normal is right on. I went the extra mile to insulate the engine compartment to minimize heat escaping into passenger area. Although the engine runs at about 195 deg I expect it remains quite warm for a long time after shutdown. This would be another piece in the puzzle. Thanks
     
  13. A phenolic spacer under the carb may help. I put them under the Edelbrock 500's on my Cad 390 and it made a big difference on hot starts.
     
  14. pull toy
    Joined: Aug 22, 2013
    Posts: 81

    pull toy
    Member

    This carb was bought new and has less than 3000 miles on it so adding the insulation plate under the carb would be a step in the right direction. Thanks
     
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  15. ProtoTypeDesignFlauz
    Joined: Jul 29, 2007
    Posts: 1,116

    ProtoTypeDesignFlauz
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    Yep, pure and simple, it is just caused by evaporation. ;)
     
  16. pull toy
    Joined: Aug 22, 2013
    Posts: 81

    pull toy
    Member

    Don't notice a gas smell in the oil but can the Edelbrock leak from the bottom into the intake like the old Q-jet from the assy bolts?
     
  17. The solution to an electric fuel pump safety issue is to wire it through a dash or under-dash push button switch. Branch the fuel line off before a new check valve to the electric pump and tie back in after the check valve. That way the mechanical pump doesn't have to pull through the electric pump
     
  18. TRENDZ
    Joined: Oct 16, 2018
    Posts: 310

    TRENDZ

    It does evaporate. The large vent of the edelbrock carb lets it happen very rapidly.
    The hotter the temp, the quicker the loss of fuel happens. I took the top off of one after a drive to see it. In 1 hour, half of the fuel level was gone. It took almost 5 hours total for the fuel to be absolutely gone. That’s with the carb top off though. With the top on, it probably would take a bit longer. C3328357-01B8-4766-9384-347024F61003.jpeg
     
  19. Callmaker
    Joined: Feb 17, 2020
    Posts: 113

    Callmaker
    Member

    Had.... the same problem!! No longer have it since I put a check valve in the fuel line. Everyone I spoke with said the same, evaporation, but at the time I had a clear filter up next to the carb, you could see it slowly draining back to the fuel tank..Check valve fixed it.
     
  20. onetrickpony
    Joined: Sep 21, 2010
    Posts: 513

    onetrickpony
    Member
    from Texas

    I agree that drain back is not very likely but it would be easy to test. Rig up a way to pinch off the rubber hose.
     
  21. carbking
    Joined: Dec 20, 2008
    Posts: 3,087

    carbking
    Member

    Drain back of the fuel in the FUEL LINE ONLY is possible with an electric fuel pump. The inlet check valve in a mechanical fuel pump will prevent this.

    For fuel to drain out of most carburetors made AFTER 1930, the car would need to be either parked on its top on in a gravity anomaly. Gasoline doesn't run uphill (fuel valves are ABOVE the fuel).

    In the FWIW category, end bowl Holleys and Autolite 4100s have less problems with evaporation due to there being an air-gap between the heat of the engine, and the carburetor bowls.

    Much as I love my Carter AFB's, they are the second worst for evaporation; only the less-dense e imitations are worse.

    Jon.
     
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  22. carbking
    Joined: Dec 20, 2008
    Posts: 3,087

    carbking
    Member

    Rethinking my previous answer:

    Some thought it possible for the earliest Rochester Q-Jets with the windowed fuel valves only, to drain a portion of the fuel in the bowl. The inlet check valve in the mechanical fuel pump prevented this, but believed fact often is more important than fact. ;)

    To counter the complaints, Rochester replaced the original inlet filter with a filter which had an enclosed check valve, which mostly silenced the critics. It didn't really solve an issue, because no issue actually existed!:p

    The Q-Jets, up through and including the 1967 versions were prone to leakage through the bowl passage access plugs. This was the real issue that the fuel inlet acquired blame. Again, Rochester listened, and changed the construction of the plugs, solving the issue.:)

    The only siphoning issue that immediately comes to mind is the Holley model 4000. The secondary air vents in the bowl cover have two functions: (1) add air to the secondary fuel, and (2) break the siphoning action when the secondary is closed. Holley published a service bulletin on this issue, that the owner should be aware of the issue and check the secondary air vents periodically so to assure they were not plugged with dirt. These bulletins were issued in the mid-1950's. Indoor plumbing was not prevalent in the area where I was raised until the 1960's. Paper that was not slick, like the Wards and Sears catalogues, was valuable! Corn on the cob was also quite popular! :p:eek:

    The carburetor that is responsible for the whole "bowl leaks down" debacle; is the Holley type AA-1 (lovingly referred to by many on this forum as the Ford/Holley model 94). This model has the power/economizer valve (a diaphragm) located in the bottom of the bowl, WITH A DIRECT PASSAGE TO THE INTAKE MANIFOLD! A backfire would often destroy the neoprene of the valve, and allow a direct leak into the intake manifold.:(

    Jon.
     
    Last edited: Apr 23, 2021
  23. Paul
    Joined: Aug 29, 2002
    Posts: 15,394

    Paul
    Editor

    I suspect too much heat in the engine compartment, too much heat transfer from engine to carb body, high alcohol content gasoline and possible low float level.

    Try to get more air movement through engine compartment, even after shut down, that's a bit bigger engine than was in there originally. Twice the energy (heat) generated and twice mass (heat sink).
    Put a wood or phenolic riser under the carb to heat isolate the aluminum Edelbrock from the iron? manifold.
    Check float level.
    I don't know what you can do about the fuel, aside from switching brands or adding stabilizers.
     
  24. 1971BB427
    Joined: Mar 6, 2010
    Posts: 6,899

    1971BB427
    Member
    from Oregon

    I'd be very concerned about a carb that siphoned all the gas out in 24 hrs! My concern is the engine oil is being severely diluted, and will cause a bearing failure if the problem isn't fixed! I wouldn't drive or start the engine until the problem is fixed, and I'd make sure to change oil and filter before starting it again! I bet pulling the dipstick and giving it the sniff test will result in gassy smelling oil already.
     
  25. jimmy six
    Joined: Mar 21, 2006
    Posts: 9,443

    jimmy six
    Member

    I’ll make another comment. If the fuel evaporates that fast it seem to me you would smell it. I run dual quads on my Ford; Carter WCFB’s with huge gas bowels on 8 corners and the exhaust heat in the manifold. I drive my car every weekend; I start it after it sits a week with one full pump and it starts immediately. The next morning I don’t even touch the foot feed. I never smell gas in my garage. I use 3/8” phenolic spacers under each carburetor. Whether it helps or not I use 1 oz or fuel conditioner with every fill up. Opps more than one comment.
     
  26. gene-koning
    Joined: Oct 28, 2016
    Posts: 2,417

    gene-koning
    Member

    Though off topic for this board, the Carter Thermoquad (and other carbs I've seen) have plugs on the bottom of the carb base that cover where the passages inside the carb were drilled. I've seen discoloration at these plugs on carbs that had a "drain down" problem before that would indicate a possible fuel leak point. In the past I've sealed the area these plugs were in with a two part epoxy that seems to make a huge difference in the carb's drain down issue. To be fair, the plugs were epoxied at the same time the carbs were rebuilt, so the rebuild could have been what solved the issue, but I can't imagine the epoxy didn't help, it it was a pretty inexpensive gesture. Gene
     
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  27. Thermoquad is an excellent carb,,,,if worked correctly .
    You can rebuild one,,,and like you said,,,,give it some attention,,,,it will work great .
    Plastic body and all,,,,great heat insulated.

    Tommy
     
  28. ProtoTypeDesignFlauz
    Joined: Jul 29, 2007
    Posts: 1,116

    ProtoTypeDesignFlauz
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  29. carbking
    Joined: Dec 20, 2008
    Posts: 3,087

    carbking
    Member

    The O/T thermoquad DOES have a leakage problem, but ONLY WHEN the owner cheaps out with a cut-rate rebuilding kit using O-rings.

    I have an 850 on my O/T 350.

    Jon
     
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  30. Bert Kollar
    Joined: Jan 10, 2007
    Posts: 1,043

    Bert Kollar
    Member

    My 360 Mopar did the same thing, boiled off the fuel. Installed a phenolic spacer and it solved the problem. Next time I would use an air gap manifold
     
    jimmy six likes this.

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