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Help Me Understand My Fuel Delivery

Discussion in 'Flat Fender Tech' started by Buster1, Nov 3, 2021.

  1. Nov 3, 2021
    Buster1

    Buster1 Member

    Ft Worth
    Joined:
    Aug 8, 2021
    Messages:
    53
    Hey guys. The previous owner did a great job getting the fuel system up and running when he pulled the M38 from a barn last year. It runs strong and seems to be fine (except for sometimes dying after cold start with throttle application, that’s possibly me not letting it warm up enough).

    Can you help me understand my setup better, and where it could also be improved? The tank is not original and I hope to replace it soon, then run snazzy braided fuel lines to the carb. And maybe hide the pump under the seat.

    Below is my setup. How can we make it better?

    I have a simple Carbole 12v 1-2A, 4-7psi, 35 gph micro electric fuel pump on switched power obviously. It sits about 12-18” from the tank.

    E1DAF510-B365-4D79-9FB1-DD1F83D8BBCC.jpeg

    From there we run fuel up to the engine area. Through an inline filter (orange circle) to a pressure regular which seems to always read 2-3 psi. From there, fuel goes to the carb.

    CF61BC1B-84F5-419F-BCCE-3F65F6A353C3.jpeg
    1B5B50E7-E74A-42B3-A8E5-3E838EA9C57E.jpeg
    Ideas and improvements welcome! Thanks!
     
  2. Nov 3, 2021
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Hills of NH
    Joined:
    Aug 3, 2003
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    8,463
    Sounds right at 2 to 3 psi.

    A safety inspector would go into full arrest upon seeing pressure-fed rubber lines in the passenger space. Not a great idea under the hood, either.

    Braided lines can chafe anything they rub against. Hard (steel not copper) lines would be best wherever possible. 1/4" brake tubing will work.
     
  3. Nov 3, 2021
    ojgrsoi

    ojgrsoi Retired 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Weatherford, TX
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    Dec 30, 2002
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    2,178
    Well if it was mine I would put the original fuel pump back on the block and use stock fuel lines. I suspect it would work. I think the electric fuel pump was added because the FLAPS in Fredericksburg didn't have a stock fuel pump but did have the electric when the old pump quit. That route would certainly clean up the area inside of that street side fender. Maybe someone would loan you a mechanical pump to test.

    If you go with a new fuel tank and stay electric, the pump can go underneath on the frame and then plumb the lines to the carb.
    Some will debate this but the electric does make it easy to start after sitting. Also, I don't know if the pressure regulator is necessary for that pump. I think it is a low pressure pump. I just never got that far. Someone stole.....oh never mind.
     
    Downs, Lockman and Buster1 like this.
  4. Nov 3, 2021
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Hills of NH
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    If it's anything like the YF on an F-head, anything over 3psi is problematic. Especially in rough terrain.
     
    Downs likes this.
  5. Nov 4, 2021
    Buster1

    Buster1 Member

    Ft Worth
    Joined:
    Aug 8, 2021
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    53
    Hey Mark. No I think the setup is great, I think electric fuel pump is the way to go, and am not sure the regulator is needed either. My guess is that it is needed due to the specs on the pump being 4-7 psi.

    I’m thinking of how to relocate everything, where to add hard lines and/or braided / PTFE lines, what to do with the px regulator, and ideas on general organization and such. I’m also investigating inexpensive electric pumps that have built in px regulation... but I know very little about that.

    Thanks to you and Pete!
     
    ojgrsoi likes this.
  6. Nov 4, 2021
    Lockman

    Lockman OK.....Now I Get It . 2022 Sponsor 2021 Sponsor 2020 Sponsor

    White City, NY 14617
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    The Electric Pump & regulator will enhance the starting ability 'cuz the FP is constant. Like Pete says...... You need to the regulator to keep the FP low for your engine. Too much FP will flood you & run way rich. Too little FP is bad too. Also, some seafoam & a Fresh filter would help too.
     
  7. Nov 4, 2021
    CHUGALUG

    CHUGALUG Member

    Silverton, OR
    Joined:
    May 11, 2019
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    203
    The pump should be at the level of the bottom of the tank. Mount it on the back of the Riser in the floor and run the fuel line through the frame up to the regulator.
     
  8. Nov 4, 2021
    duffer

    duffer Rodent Power

    Bozeman, MT
    Joined:
    Sep 17, 2009
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    A low mounted pump is desirable but most low pressure electric pumps have sufficient "suck" ability that that isn't usually a problem. I seem to remember old Subarus had the pump on the firewall. The high pressure EFI

    external pumps are a different story.

    I would not use steel for fuel lines. That was ok before ethanol but with the present gasoline supply, it's a guarantee for rust. I think the copper/nickle brake line tubing would work well. I second the opinion on the presence of any fuel lines in the passenger space, most especially pressurized fuel lines. There is a reason fuel pressure gauges are almost exclusively electrical. Self immolation in any sort of serious accident.
     
  9. Nov 4, 2021
    Buster1

    Buster1 Member

    Ft Worth
    Joined:
    Aug 8, 2021
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    Thanks guys!!

    @CHUGALUG can you describe which riser and a little more detail about your suggested path?

    I’m also trying to find where the original fuel line routing was in the M38 and I might try to replicate that. I very much like the idea of going below the body and thru the frame rail to the engine area.
     
    Last edited: Nov 6, 2021
  10. Nov 4, 2021
    Downs

    Downs Kubota Orange Rattlecan

    Hunt County Texas
    Joined:
    Jul 25, 2020
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    If it was my Jeep I'd convert back to a stock fuel system and leave it. If you feel the need to add an electric pump inline somewhere put it on switched power and only run it long enough to prime the carb, the mech pump can pull fuel though those style of electric pump. I converted my 76 back to the stock mech pump and couldn't be happier with it. Those little chatter box pumps can get annoying. And it gets driven at least once a week and I've had no issues with the carb bowl draining or drying up.
     
    PeteL likes this.
  11. Nov 5, 2021
    jeepdaddy2000

    jeepdaddy2000 Member

    Eagle Point oregon
    Joined:
    Jun 24, 2004
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    739
    I agree with reverting back to the stock setup.
    A couple of things to think about with your current setup:
    Routing fuel systems inside the cab is a big no no. Any rupture, especially on the pressure side and you are awash with gas.
    Mounting a fuel pump close to where you can kick it seems like a recipe for disaster.
    Any vehicle running an electric pump as a primary pump needs a roll over valve and/or cut off that shuts down with the engine. This, for obvious reasons, keeps the pump from running in case of a catastrophe.
     
    Downs likes this.
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