Fuel Return Line

Discussion in 'Flat Fender Tech' started by Patrick, May 20, 2016.

  1. May 20, 2016
    Patrick

    Patrick Super Moderator Staff Member Sponsor

    Los Alamos, NM
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    So the flatty still has the issue of flooding after I shut it off when it's hot. At this point I've done a lot of things to try to cure it, but to no avail. Right now I think it's heating up the fuel in the line from the pump to the carb to the point of pushing the needle and seat open and overflowing the float bowl. I believe a return line from right before the carb back to the tank might fix it, along with helping what little vapor lock I sometimes get while it's running. Now, I'll have to include a fairly small orifice where the return T's off of the fuel line so that the pump doesn't just pump all the fuel back to the tank, thereby not supplying the carb with enough fuel. I'm thinking .050" or so orifice. Any thoughts? Too big? too small? Does this all make sense?
     
  2. May 20, 2016
    wheelie

    wheelie beeg dummy Sponsor

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    Is it possible to insulate that fuel line somehow?
     
  3. May 20, 2016
    47v6

    47v6 junk wrecker! Sponsor

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    Maybe a fuel pressure regulator and a heat shield?
     
  4. May 20, 2016
    Patrick

    Patrick Super Moderator Staff Member Sponsor

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    Been there, done that.
     
  5. May 20, 2016
    Patrick

    Patrick Super Moderator Staff Member Sponsor

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    Been there, done that. :)
     
  6. May 20, 2016
    Patrick

    Patrick Super Moderator Staff Member Sponsor

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    Regulator won't help fuel pressure increase from heat, when the engine isn't running.
     
  7. May 20, 2016
    Patrick

    Patrick Super Moderator Staff Member Sponsor

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    I was actually looking for opinions on orifice size in the return line I'm going to plumb in..;)
     
  8. May 21, 2016
    SFaulken

    SFaulken Member

    Renton, WA
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    Yeah, .050 sounds pretty reasonable. Better to start small anyway, you can always enlarge it later, if it's not returning enough fuel to fix the issue
     
  9. May 21, 2016
    45es

    45es Sponsor Sponsor

    Naches, WA
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    Need to know the fuel pump discharge pressure to accurately predict orifice size. If for example the pump pressure is 5 psig and you use a 0.050" orifice the flow thorough orifice (return line) will be approximately 0.1 gpm.
     
  10. May 21, 2016
    timgr

    timgr Jeepin' Nerd Sponsor

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    Why not use one of the fuel filters with three nipples designed for this purpose? The TSM should tell you the expected pressure from the fuel pump, and one of the later Jeep applications will supply the filter. The 6s are 3-5 psi and the V8s are 6-8 IIRC ... something like that. I would just try the 3-nip filter from a 258 - very likely to work fine.

    More Information for WIX 33040
     
  11. May 21, 2016
    Patrick

    Patrick Super Moderator Staff Member Sponsor

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    I could, but I really don't want to put any rubber fuel hose on the supply side. I have hard line all the way into a Carter sediment bowl/ sintered metal filter.
    The fuel pump puts out about 3.5PSI
     
  12. May 21, 2016
    timgr

    timgr Jeepin' Nerd Sponsor

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    Cut the flares off of the fuel filter and connect with a compression fitting? No rubber lines then.
     
  13. May 21, 2016
    Patrick

    Patrick Super Moderator Staff Member Sponsor

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    I could. It's just that the sediment bowl is attached to the side of the carb by a 1 1/2" long brass pipe. I wanted to make a Tee that replaces that pipe, with a fitting for the return, with orifice in it.
     
  14. May 21, 2016
    Patrick

    Patrick Super Moderator Staff Member Sponsor

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    The only pic I could find...[​IMG]
     
  15. May 21, 2016
    Patrick

    Patrick Super Moderator Staff Member Sponsor

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    I wonder if I could go get said fuel filter, and cut it apart and find/ measure the return orifice?
    I do know the return orifice on a dauntless fuel pump is pretty small.....
     
  16. May 22, 2016
    colojeepguy

    colojeepguy Colorado Springs Sponsor

    At the foot of...
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    Ford used a tee fitting with a return orifice on carb'ed 460's in the 80's.
    IIRC they had double flare fittings, 5/16 for inlet and outlet and 1/4 for return, and they had 3 different orifice sizes- .040, .060, & .090. (don't take those numbers for gospel but it was something like that)

    Edit:found some more info after I remembered the part numbers....

    E0TZ9N176-B .090 Used as a field fix for units experiencing hot fuel problems.
    E3TZ9N176-A Red Dot .060 For Fuel Starvation or Power Loss.
    E3TZ9N176-B Blue Dot .040 For Fuel Starvation or Power Loss.
     
    Last edited: May 22, 2016
  17. May 22, 2016
    Patrick

    Patrick Super Moderator Staff Member Sponsor

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    Interesting....Thanks Doug!
     
  18. May 25, 2016
    Patrick

    Patrick Super Moderator Staff Member Sponsor

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    So here's what I did. I added the "T" between the filter and the carb. The nipple for the return line, I soldered shut and drilled a .044" hole. I've only driven it about 10 miles, and shut it off three times for a few minutes each time. So far, it has not had any of the old symptoms, and apparently the .044" hole isn't too much because it is not starving for fuel. When I get a chance, I'll run it up the mountain on a warm day and see how it acts.[​IMG] [​IMG] [​IMG]
     
  19. May 26, 2016
    WorkInProgress

    WorkInProgress Member

    Kennewick, Wa
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    i wonder if your flooding after shutoff is heat soak related, and might have something to do with how close the coolant hoses are to your carb, lines, and fuel filter.
    my 48 cj2a also floods out sometimes after shutting off.

    i have thought of at least for now in the summer plugging off the heater hoses at the water pump and at the head to keep those hot hoses away from the carb and fuel lines and see if that helps. but also my mechanical temp gauge shows my temp gets to like 215 degrees after shut off so i was also thinking of removing my 180 degree thermostat and replacing it with a 160 for the summer. but i also dont have a fan shroud attached to my new aluminum radiator which i need to install one of these days
     
  20. May 26, 2016
    Patrick

    Patrick Super Moderator Staff Member Sponsor

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    No, because in the summer, when it acts up, the heater valve is off so those hoses are cold.
     

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