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Technical Fuel pressure

Discussion in 'Traditional Hot Rods' started by robert graves, Apr 22, 2020.

  1. robert graves
    Joined: Nov 2, 2018
    Posts: 62

    robert graves

    Having a terrible time trying to get fuel pressure to set and stay at 3 psi to flathead ford v8 with dua carbs
    , help!
     
  2. big duece
    Joined: Jul 28, 2008
    Posts: 5,916

    big duece
    Member
    from kansas

    Which regulator are you using? Malpassi has a fuel filter and regulator that's 1-7psi. Hard to get in the states, but used for Webers in the VW world.
     
  3. clem
    Joined: Dec 20, 2006
    Posts: 2,860

    clem
    Member

    More details required please, type of carb, type of fuel pump etc.....
     
  4. robert graves
    Joined: Nov 2, 2018
    Posts: 62

    robert graves

    Holley adjustable 1-6 psi, set it at 3 psi but keeps going to 1 psi on mechanical pump 1946 model 59 an engine then it won't adjust any higher
     
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  5. robert graves
    Joined: Nov 2, 2018
    Posts: 62

    robert graves

    Speedway carbs on the 97 style ,have tried 2 different mechanical pumps and also tried a Holley ,variable 1-6 psi with same effect , tank cleaned and coated,all new lines with 2 fuel filters in the system ,set to 3 psi then drops to zero after a minute or two of run time ,then I cannot get pressure to increase
     
  6. robert graves
    Joined: Nov 2, 2018
    Posts: 62

    robert graves

    The
    The electric pump is a 9 psi and the regulator is a 1-6 variable
     
  7. alchemy
    Joined: Sep 27, 2002
    Posts: 15,515

    alchemy
    ALLIANCE MEMBER

    You have the gauge mounted right on the regulator?
     
  8. Petejoe
    Joined: Nov 27, 2002
    Posts: 10,466

    Petejoe
    ALLIANCE MEMBER
    from Zoar, Ohio

    With that statement it’s obvious you have a blockage somewhere.
    Install your pump and regulator near your tank.
    The blockage could very well be at your tank, line , filter or regulator.
    Maybe something came off your new tank lining??
     
  9. 19Fordy
    Joined: May 17, 2003
    Posts: 6,814

    19Fordy
    Member

    Petejoe, has some good suggestions.
    Also:
    Disconnect the fuel line at the carb, turn on the pump and actually
    see how much gas is being pumped to your carbs.
    Also:
    Would it be possible to by pass the regulator and have the pump send the gas
    directly to the carbs?
    Also:
    Is the diaphragm in your regulator faulty? Is it leaking? Take your
    regulator apart and check for cracked diaphragm.
    Finally:
    It has been noted on Fordbarn that the viscous filled fuel pressure gauges mounted in the engine
    compartment often drop to ZERO reading due to the engine heat. When I emptied the fluid from
    my engine compartment fuel pressure gauge I obtained more accurate readings. The needle movement
    fluctuated so I added a small amount of brake fluid to the gauge without filling it. There was improvement.
     
  10. Doublepumper
    Joined: Jun 26, 2016
    Posts: 607

    Doublepumper
    Member

    If you have a filter before the pump, you might try bypassing it. It's possible it could be restricting flow to the pump.
     
  11. Blues4U likes this.
  12. robert graves
    Joined: Nov 2, 2018
    Posts: 62

    robert graves

    Gage is mounted in line right before the carb
     
  13. robert graves
    Joined: Nov 2, 2018
    Posts: 62

    robert graves

    I did blow air pressure through the line to the tank with cap still on and the back pressure sent a big stream of fuel back to me at the carbs , checking for blockage
     
  14. robert graves
    Joined: Nov 2, 2018
    Posts: 62

    robert graves

    I hadn't tried moving the electric pump close to the tank yet to push fuel instead of pull ,and what Gage is recommended at the carbs ,1-15 oil filled or dry or other ones
     
  15. alchemy
    Joined: Sep 27, 2002
    Posts: 15,515

    alchemy
    ALLIANCE MEMBER

    Dickster sells a low pressure gauge here in the classifieds. Anything with a large range won't be accurate when you are trying to measure clear down on one end of the scale.

    I also agree that the pump should be as close to the tank as possible.
     
  16. jimmy six
    Joined: Mar 21, 2006
    Posts: 6,356

    jimmy six
    Member

    Is it running out of gas while you are driving or under full throttle?
     
    Blues4U likes this.
  17. robert graves
    Joined: Nov 2, 2018
    Posts: 62

    robert graves

    It starts missing badly shortly after idle like it's starving ,idle is great ,but always misses at hard acceleration, engine is new rebuilt 60 over on bore,max 1 cam,pertronix electronic in crab ,with hot coil ,new wires,cap
     
  18. 19Fordy
    Joined: May 17, 2003
    Posts: 6,814

    19Fordy
    Member

    Remove the gas tank cap and THEN blow air through the line.
     
  19. big duece
    Joined: Jul 28, 2008
    Posts: 5,916

    big duece
    Member
    from kansas

    The speedway 97s have not gotten the best reviews, make sure the accelerator pump is giving the "shot" you need. Might need to completely disassemble and check for debris.
     
  20. King ford
    Joined: Mar 18, 2013
    Posts: 1,345

    King ford
    ALLIANCE MEMBER
    from 08302

    In our racing application ( northeast bigblock modifieds) many of us have had trouble with any sort of " deadhead " pump or regulator. When a pump of greater volume and pressure than could ever be required and a " bypass" style regulator which returns the excess fuel to the tank is used WAY fewer fuel pressure/delivery issues are encountered.
     
  21. Aaron D.
    Joined: Oct 27, 2015
    Posts: 720

    Aaron D.
    Member

    I had a similar problem with the same symptoms as you have. I found my front carb inlet had a bunch of debris in it. The front carb bowl would run out of gas after awhile and the motor would run on just the back four cylinders. Unscrew the tops of the carbs so you can see the float bowls, blow air in the inlet( don't spray fuel everywhere) to the carbs to make sure the inlets are not clogged. Hook up your fuel lines again and turn on your fuel pump, see if both float bowls are filling up. If both fill up, put it all back together and try it.
     
  22. robert graves
    Joined: Nov 2, 2018
    Posts: 62

    robert graves

     
  23. robert graves
    Joined: Nov 2, 2018
    Posts: 62

    robert graves

    Here's an update on my fuel pressure problem, I moved the electric fuel pump and mounted It on the frame about 12 inches from the fuel tank outlet with a 100 micron filter between them , wired through a relay to the starter switch and ground wire directly to the battery ground, turned the key on and got 9 psi on both the carbs gages, adjusted the regulator down to 3 psi recommended for the speedway 97 knockoffs , and started right up ,didn't get a road trial in due to heavy rain today, but gages only fell to 2 psi after heated up , will know more Monday after road trial ,thanks to everyone for the helpful information, was a Lotove good help.
     
  24. robert graves
    Joined: Nov 2, 2018
    Posts: 62

    robert graves

     
  25. big duece
    Joined: Jul 28, 2008
    Posts: 5,916

    big duece
    Member
    from kansas

    I think your fine in the 2-3 range. If a guy had a return line back to the tank that had a .030 orifice in the hose, the pressure would bleed off right after the pump shots off, and would eliminate any heat soak boil overs. I'm planning to do that with my Webers.
     
    town sedan likes this.
  26. robert graves
    Joined: Nov 2, 2018
    Posts: 62

    robert graves

    My biggest beef about it all is I bought 2 different new fuel pumps ( mechanical) made in China junk and neither would give me more than 1 psi , the quality comming across the pond is awfull, so if you run mechanical I suggest having it built by a specialist in the USA or rebuild it yourself with quality parts.
     
    town sedan likes this.
  27. robert graves
    Joined: Nov 2, 2018
    Posts: 62

    robert graves

    I also plan to add a tank return
     
  28. big duece
    Joined: Jul 28, 2008
    Posts: 5,916

    big duece
    Member
    from kansas

    thumbnail (22).jpg thumbnail (9).jpg thumbnail (22).jpg thumbnail (9).jpg
    I used an old stromberg jet, and threaded the ID of a brass fitting to accept it. You can soldier the hole shut and drill it whatever you want.
     
    61cad, Jet96, town sedan and 3 others like this.
  29. alchemy
    Joined: Sep 27, 2002
    Posts: 15,515

    alchemy
    ALLIANCE MEMBER

    I don't know anything about Speedway Super7's except what I've read on the internet. But if they think they behave anything like a Stromberg does, they should have 2 pounds maximum. My real Strombergs behave best with 1.5 pounds at the gauge on the firewall.
     

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