no fuel to carb on crank

Fuel and Air Systems

  1. Tarek Baratta

    Tarek Baratta Active Member

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    when i try to start my 1975 Plymouth Valiant 318 after letting it sit for a few days it cranks, starter engages fine, but no firing, pour fuel down carb starts dies 10 seconds later, repeat a few times, run time gets longer until it maintains a idle, my guess is after a while fuel is flowing back down the line into the tank, as no smell of fuel or leaks on the ground, but not sure, any ideas?
     
  2. Dana67Dart

    Dana67Dart Like a fine wine, only getting better with age! FABO Gold Member

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    The fuel pump should have a back flow check valve.

    To be sure next time it has sat as described. Pull the hose from the carb, extend it to a sutable container at carb height and have someone crank the engine. If you don't get almost immediate flow, I would suspect the fuel pump.
     
  3. Tarek Baratta

    Tarek Baratta Active Member

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    thanks for the quick reply, will check that next time
     
  4. Dana67Dart

    Dana67Dart Like a fine wine, only getting better with age! FABO Gold Member

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    Does it only happen if the engine has come up to operating temp then shut down (Fuel line too close to an exhost pipe could vapor lock)
     
  5. dano

    dano Evil Handy Man

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    The fuel evaporated out of the bowls. It will do what it's doing until they/it are full enough to maintain running. Some put a small electric prime pump in to aid in filling.
     
  6. pishta

    pishta I know I'm right....

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    Install an electric. If you take the feed off the pump and are able to pull and hold a vacuum, you should be ok. Been stated that lines cannot pull fuel from the carb via the lines as they fill bowl from the top. What carb you running, AFB or TQ?
     
  7. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    Make sure the fuel evap control is intact and venting properly. The 1/4" tube coming from the tank --up into the engine bay--and interfacing with the carbon can system IS THE VENT on those cars. Also you must have the proper "pressure vacuum" fuel cap. If any of that is disconnected/ plugged/ etc etc you might be pulling a vacuum in the tank, causing the think to "suck" fuel back.

    Latest shop manual I know of for free download is the 73, and there might be "some stuff" different RE the evap system, but you can download it from MyMopar
     
  8. Tarek Baratta

    Tarek Baratta Active Member

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    thanks, it has an edlbrock carb, was installed when i bough the car, will check all that next time i get a chance
     
  9. RustyRatRod

    RustyRatRod Weenie idiot loser. FABO Gold Member

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    Assure it has the THICK (Over .300") insulator gasket under it. If it does not, it is likely vaporizing the fuel out of the fuel bowl. They must have that gasket to keep that from happening.
     
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    • 70aarcuda

      70aarcuda Master Hoader of SBM FABO Gold Member

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      edelbrock are the worst about evaporating out of the bowls. Been there done t hat
       
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      • RustyRatRod

        RustyRatRod Weenie idiot loser. FABO Gold Member

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        Since they don't have a gasket between the throttle body and the main body of the carburetor, they lack an extra layer of insulation, so the bowl gets too hot, unless you run that really thick carburetor mounting gasket. That makes up the difference.
         
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        • 70aarcuda

          70aarcuda Master Hoader of SBM FABO Gold Member

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          Small bowls... and squirter well is not on the floor of bowl like a Holley so it loses it pump shot before the bowl is empty...electric pump solves the problem...or spin the engine over every day
           
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          • RustyRatRod

            RustyRatRod Weenie idiot loser. FABO Gold Member

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            I have let my truck sit two months. Go out, hit the gas five or six times and it busted right off. Now I have the little Street Demon 3 barrel on it and it has the extra gasket on top of the throttle body so it has the little extra insulation.....plus I still have the thick mounting gasket too. Could have something to do with location as well. Here, it's only a maximum of 10% ethanol. Other places may have more, so that certainly has an effect.
             
          • d55dave

            d55dave Well-Known Member

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            It is physically impossible for fuel to leave the float bowl and travel down the fuel line to the tank. As said above, the fuel is evaporating out of the float bowl. Modern fuels contain a lot of ethanol which vaporizes easily. When the car has been sitting for a few days first crank the engine for ten seconds or so, then stop and pump the gas four or five times to prime the engine and set the choke, then start it.
             
          • Dana67Dart

            Dana67Dart Like a fine wine, only getting better with age! FABO Gold Member

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            if OP has to do this "a few times" I suspect more than a dry fuel bowl. assuming all other things are working correctly. 10 seconds of run time should fill the fuel bowl.

            assuming 600 rpm at idle (which is 10 rps, 600/60)
            10 seconds of idling
            the crank rotates 100 time
            fuel pump is off the cam so 100 / 4 = 25 revolutions or 25 pumps for the fuel pump
            That should be enough to fully fill the fuel bowl
             
          • ted_sweet

            ted_sweet Well-Known Member

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            fuel evalorationg wont do what he described
             
            Last edited: Dec 11, 2019
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            • Tarek Baratta

              Tarek Baratta Active Member

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              tested, no fuel at pump, replaced pump and it fixed the problem, it's now pump pump crank, pump pump crank, start
               
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              • Dana67Dart

                Dana67Dart Like a fine wine, only getting better with age! FABO Gold Member

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                That sounds right.

                I usually do pump pump crank pump crank start die crank start neutral reverse. (904 trans)
                 
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                • TF360

                  TF360 Well-Known Member

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                  What pump did you go with?
                   
                • TF360

                  TF360 Well-Known Member

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                  How did you test it?
                   
                • Tarek Baratta

                  Tarek Baratta Active Member

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                  test just cranked the motor with the line feeding into a container, then after 2 minutes of nothing took off line at pump and nothing, for new pump whatever lordco (local parts store) gave me, still mechanical
                   
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