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What's The Purpose Of Using A Mechanical And Electric Fuel Pump?

Discussion in 'Early CJ-5 and CJ-6 Tech' started by Matt Mitchell, Nov 30, 2018.

  1. Nov 30, 2018
    Matt Mitchell

    Matt Mitchell Playin w/My Willy

    Idaho Pan Handle
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    I have a 62 Willys with a Chev 350 conversion. At the time of purchase, it had the mechanical fuel pump on the engine AND an electric pump installed, both functioning. The electric pushes fuel to the mechanical then to carb. I have never seen this type of install before... On anything. Is there a reason I am unaware of? Was thinking maybe steep incline/decline while running trails?
     
  2. Nov 30, 2018
    Oldiron90

    Oldiron90 New Member

    Colorado Springs, CO
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    You should be good with just the mechanical pump. I prefer mechanical pumps... had bad experiences with in line electric pumps + they're loud most of the time.

    I can't think of a good reason why someone would have installed one to feed a mechanical pump.
     
  3. Nov 30, 2018
    Matt Mitchell

    Matt Mitchell Playin w/My Willy

    Idaho Pan Handle
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    Thank you! My thoughts as well.
     
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  4. Nov 30, 2018
    ITLKSEZ

    ITLKSEZ Volvophilic

    Post Falls, ID
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    Sounds like the guy was having delivery issues with just the manual pump, so rather than do the right thing and replace it, he just added another booster.

    Problem is, a failing manual pump can leak gas into the crankcase, and the electric pump might be making it worse.

    Replace the manual pump and delete the electric one, or just delete the electric one and see if it works without it.

    I like the noise of the electric pumps because they get loud when you're about to run out of gas. Gives you a heads up. :D
     
  5. Nov 30, 2018
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member Sponsor

    Denver, CO
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    Exactly as said above
     
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  6. Dec 1, 2018
    colojeepguy

    colojeepguy Colorado Springs Sponsor

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    It used to be common to install an electric pump to cure vapor lock. No reason why it won't work just fine as long as it's installed properly. Electric pump should be as close as possible to the tank.
     
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  7. Dec 1, 2018
    timgr

    timgr Jeepin' Nerd Sponsor

    Medford Mass USA
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    For cars that sit idle a lot, an electric fuel pump makes starting easier. It overcomes the "dry bowl syndrome" that carburetors will have when sitting for a long time.

    If I wanted electric, I would just convert to electric and not run both.
     
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  8. Dec 1, 2018
    70cj5134f

    70cj5134f Member

    East Tn
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    I have this setup on my 1970 amc rebel, 455 Pontiac power car.
    Reason, if it sat for more than a day, it took 20-30seconds grinding on starter to start.
    With the elect pump, plumbed in line, I just turn it on a few seconds and it starts right up.
    Then the mechanical pump works by it self.
    I Also used it when racing, engine would run out of fuel, just before red line .
    Ps it's a suck through pump, allows the mec pump to pull fuel through it when off.
    Lots of my classic car friends use this setup. Saves grinding on starter.
    Didn't have this problem back in the day. Modern fuel evaporates and perculates
    way faster than 70s fuel.
     
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  9. Dec 1, 2018
    Henri Watson

    Henri Watson New Member

    Mississippi
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    Agreed, electrics are useful for vehicles that sit and lose prime over time. Rather than take the air filter off and pour a shot of gas in the carb to get going you can just turn the key on for a few seconds then fire it right up. I just made the switch for that exact reason.
     
  10. Dec 1, 2018
    Alan Rogers

    Alan Rogers New Member

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    I run both on my v8 power CJ. use electric on first start up. And It really comes in handy at freeway speeds pulling hills and in vapor lock issues. other than that it is usually off. just running with mechanical pump.
     
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  11. Dec 1, 2018
    Sierra Bum

    Sierra Bum Member

    The High Sierra
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    Question then:
    Aside from a failing mechanical pump potentially leaking gas into the crankcase and not knowing it, are there any downsides to running both? And are most of the basic aftermarket electric pumps "pull though"?...put it on a toggle switch, use it to prime and and then turn it off.

    Seems like a good solution to slow starting and perhaps as a back-up as well...
     
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  12. Dec 1, 2018
    Oldriginal86

    Oldriginal86 Member

    Pasadena, Md.
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    Could be the eccentric is worn on the camshaft. Rare but it happens. Easy to check on a sbc.
     
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  13. Dec 1, 2018
    colojeepguy

    colojeepguy Colorado Springs Sponsor

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    Most are not...they need to run all the time. There are some that are able to draw through.
     
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  14. Dec 2, 2018
    70cj5134f

    70cj5134f Member

    East Tn
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    My draw through came from napa, bout 35$.
    Counter guy helped pick right one.
    Not much bigger than an in line fuel filter.
     
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  15. Dec 2, 2018
    Keys5a

    Keys5a Sponsor Sponsor

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    The small cube shaped electric pumps are draw-through style.
    I have run both on vehicles, and just running the elecric pump for a minute before starting fills the bowls in the carb for quicker starting if the vehicle has been sitting a few weeks.
    -Donny
     
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  16. Dec 12, 2018
    Matt Mitchell

    Matt Mitchell Playin w/My Willy

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    All good information, thank you!! I am going to leave the set up as it is, since I am not driving it for weeks at a time. That seems to be possible reason why the previous owner put it in the Jeep in the first place. I will check the electric and make sure it is a "draw through." If not, I'll change it.
     
  17. Dec 12, 2018
    NCRenII

    NCRenII yellow fever Sponsor

    Far Nor Cal
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    I've used electric over mechanical on dual quad vehicles to stave off starvation on quarter mile runs, and only with a fuel return line.
    I don't like the idea of using an electric to be able to quickly fire off a long sitting motor. I've always liked the idea of cranking to bring up oil pressure thus avoiding dry starts.
     
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  18. Dec 12, 2018
    PeteL

    PeteL Member Sponsor

    Hills of NH
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    Exactly.
     
  19. Dec 12, 2018
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member Sponsor

    Tantallon, Nova...
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    If you consider it possible that your jeep will end up parked in a non-preferred position then a low oil pressure cutoff or a roll over switch would be a good idea, more than one rig has been BBQ'd because an electric pump got all enthusiastic about shooting gas all over a hot engine. :(
     
  20. Dec 15, 2018
    Norcal69

    Norcal69 Member

    Cottonwood, Ca
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    This is fact. Anytime my Jeep has sat overnight, I always crank it until I get oil pressure. Same as you would do with a race engine.
     

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