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Thread: Fuel Pump for Triple Webers

  1. #1
    Registered User rocketdog's Avatar
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    Dec 2004
    sedona, az

    Default Fuel Pump for Triple Webers

    I know there's lots of threads about this...and I think I've read them all. I installed my triples last year and decided to keep the stock mechanical fuel pump. It puts out quite adequate volume and pressure for the triples. I have a pressure gauge before the carbs and regulator on the tank return line which keeps the pressure at 3-4 psi. The car runs great even under heavy fuel starvation.

    My question: why does it take so much cranking to get fuel to the carbs for the engine to fire when cold and the car has sat for a while? The pump is supposed to have a check valve to prevent draining of fuel back into the tank.....correct? It seems I'm pumping new fuel from way back at the tank. I do have the stock electric fuel pump at the tank, but that doesn't kick in till the engine cranks up to a certain rpm. When warm the engine cranks quickly. I had the same problem with stock SU's....lots of cranking when cold. I know most have gone the electric pump route with inertia switches and stuff. I know the carb bowls will eventually evaporate, but the mechanical pump volume can easily fill those. (I know the fuel evaporates as my garage stinks for a day after running the car...that's a question for another thread: Stinky Webers)

    What simple, dumb thing am I over looking?
    Late 260Z; 2005 Daytona Blue paint; Triple Webers 40DCOE; competition springs w/Tokico HP shocks; Koenig 17x7 Crosshairs w/ Yokohama AVS 215/45 WR 17; Original owner; Show car w/ many awards

  2. #2
    Registered User Walter Moore's Avatar
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    Oct 2002


    You could have fuel evaporating from the lines between the pump and the carbs, as well as from the float bowls. When you try to start the car the pump has to fill the lines, and the bowls. Oh, and the fuel pump operates off on an eccentric on the cam, which turns 1/2 the speed of the motor. More volume = more cranking.
    '71 240Z, Because any fool can drive fast in a straight line.

  3. #3
    Formerly known as Koalia Reverend's Avatar
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    I did complete valve adjustment. Before that it started very badly. Now it starts right up, even in cold days! Running SU's with only mechanical pump.
    -72 240Z "Goldie"

  4. #4
    Torch Wielding Villager gogriz91's Avatar
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    May 2002
    Middle GA, for now


    If you have a 260 it also has an electric pump by the tank, is that working? Do you have a heat shield for your triples? I live in GA and it gets so hot the car can stumble at idle if I'm sitting at a light for a long period of time but I only run a Carter electric at the tank. Sometimes I let it run for 10 seconds or so before cranking when it's hot but sometimes I just have to crank it until it starts.

    Depending on the elevation I've had problems too, Yellowstone in the summer with only a mechanical fuel pump didn't work for me.
    Last edited by gogriz91; 08-08-2013 at 11:27 PM.
    '73 HLS30 129806 ; L-28, street cam, SUs, 5-speed, Koni's, Suspension techniques springs, swaybars, 3.90 R200 LSD

    Heavily medicated for your protection

  5. #5
    Registered User siteunseen's Avatar
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    Quote Originally Posted by Koalia View Post
    I did complete valve adjustment. Before that it started very badly. Now it starts right up, even in cold days! Running SU's with only mechanical pump.
    Same thing with mine!
    1972 240Z #918 New Sight Orange
    1977 280Z #305 Light Blue Metallic
    1972 240Z #110 Persimmons Red

  6. #6
    Supporting Member Zedyone_kenobi's Avatar
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    The fuel will evaportate right out of the fuel bowls. There is nothing ot stop it.
    When I turn my key and let my electric pump prime the carbs, it runs for several seconds before you hear the pump load up indicating its pushing against a dead headed system. I do not currently run a flow through system, but it is in the plans.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

  7. #7
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    Dec 2010
    Spartanburg, SC


    It appears you are in Arizona so I would think evaporation is working against you and the mechanical pump takes a while at cranking speeds to fill every thing up...

  8. #8
    Rust Free'ish zKars's Avatar
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    Jul 2006
    Calgary, AB Canada


    I'm going to be the devils advocate here. Why don't all the SU carb guys in the hotter climates complaining of similiar symptoms? Should be real common to all "float bowl" users....

    I have this issue too with my Mikuni 44's The time it takes to get it to start is directly propotional to length of time it sits. Mechanical pump or electric. 24 hours, no wait time at all. 48 hours, maybe 15 sec of cranking, 7 days, maybe 40 seconds of cranking. I have a check valve too.

    How can something this pretty be so tempermental?

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    Maybe that answers my own question....
    Last edited by zKars; 08-09-2013 at 06:32 PM.
    73 240Z HLS30 149331
    69 510 PL510 77603
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