Physically Impossible

Fuel and Air Systems

  1. TrailBeast

    TrailBeast AKA Mopars4us on Youtube

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    On fairly regular basis I see people post about their car not wanting to fire up after sitting for a day, or days.
    “I think my fuel is draining back out of the carb” ends up being mentioned.
    This is not physically possible with the average carbs we run.
    The fuel would literally have to jump up an air gap and climb back out.

    It can drain back down the line from the needle and seat, or evaporate from engine heat after shutdown, but it will never ever ever suck the fuel out of the bowl/s.
    That’s about as possible as the existence of the tooth fairy.
     
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    • dukeboy_318

      dukeboy_318 FABO Gold Member FABO Gold Member

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      I don’t know about draining out but I have had the bowls be empty after sitting for a while. Doesn’t take heat, gas will evaporate over time, which is what I’ve always chaulked it up too
       
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      • toolmanmike

        toolmanmike Moderator Staff Member FABO Gold Member

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        Exactly. Evaporation
         
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        • ragtopfury

          ragtopfury Well-Known Member

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          Idk man. A quarter miraculously showed up in place of every tooth I ever lost when I was a kid. At the rate of inflation, I can't wait for my teeth to start falling out again in another 10-20 years. There's got to be a 71 Cuda in there by then if I lose them all at the same time.
           
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          • TrailBeast

            TrailBeast AKA Mopars4us on Youtube

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            I agree that it evaporates eventually even without engine heat, but it’s the people that say it drained back to the tank from the bowls I’m referring to.
             
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            • Dicer

              Dicer The past is practice. FABO Gold Member

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              I fully agree with the statement," gas cannot be sucked out of the carburetor bowls". But still the gas can be sucked back into the tank, leaving the fuel lines and pump dry. When the gas tank cools down their is a bit of a vacuum that takes place, especially when the gas tank vent cap is not working or if some of the emission vacuum lines are plugged and or removed. I installed a check valve in the fuel line just to stop this sort of thing....
               
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              • mechanicmark

                mechanicmark Well-Known Member

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                And everybody forgets about that leaky check valve in the mechanical fuel pump that causes true drain back.
                 
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                • 66340SEDAN

                  66340SEDAN FABO Member #3649 FABO Gold Member

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                  Wait a minute, the tooth fairy isn’t real?!?
                   
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                  • clementine

                    clementine Flight risk FABO Gold Member

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                    Right? This is serious new. Enquiring minds want to know!!!
                     
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                    • Treblig

                      Treblig Well-Known Member

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                      That's why I put an axuilary electric (flow thru) fuel pump on my Barracuda. I turn the key to "on" then flip the fuel pump switch....let it pump up the fuel to the carb (and mechanical fuel pump), it helped a lot.
                       
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                      • clementine

                        clementine Flight risk FABO Gold Member

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                        When I owned the 56 coronet with a 291 hemi, that sucker needed a prime every time. Big ol cast iron intake seemed to hold the heat and had a tiny two barrel, so not a lot to evaporate.
                         
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                        • inertia

                          inertia Well-Known Member

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                          Thnx Trailbeast, I was gonna tackle that last nite, - imagine, water in your sink jumping back up to the faucet to drain !
                           
                          Last edited: Nov 20, 2021
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                          • Brooks James

                            Brooks James VET, CPT, Huey Medevac Pilot FABO Gold Member

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                            I have only seen one exclusion. My buddy was putting new 6pk carbs on a Challenger. It wouldnt start after sitting a day. The center carb had a very small casting flaw that allowed the fuel to leak out
                             
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                            • toolmanmike

                              toolmanmike Moderator Staff Member FABO Gold Member

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                              Friggen' Holley's!
                               
                            • Dana67Dart

                              Dana67Dart The parts you don't add don't cause you no trouble FABO Gold Member

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                              I'm not going to be the one to tell him!

                              upload_2021-11-20_9-32-40.png
                               
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                              • MoparMike1974

                                MoparMike1974 FABO Gold Member FABO Gold Member

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                                The problem is the ethanol in the fuel evaporates very fast. Its really a problem on the edelbrock/carter carbs. I pulled a carb apart after 2 days and the bowls were bone dry with only a little brown substance left in the bottom.
                                 
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                                • Brooks James

                                  Brooks James VET, CPT, Huey Medevac Pilot FABO Gold Member

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                                  I bought a bunch of Holleys thinking I was going to clean up rebuilding and flipping. Unless it is a double pumper, i havent been able to give them away, I just sold a very clean, rebuilt 750 vac sec that was posted for a month for $100. I think the problem might be one of several things, the market is flooded with Holleys, or holly quality control has gone down, or They are making copycat Holleys that offer more opportunities for tuning, for a Good price, new
                                   
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                                  • 67Dart273

                                    67Dart273 FABO Gold Member FABO Gold Member

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                                    Forced Alky fuel mix is the stupidest farce forced upon the U.S. ever. When I ran the carb on my 67 (vs EFI), I used a carb insulator, DIY vapor return system, and rear mount electric pump. It helped a bunch. 'N yeh, I used an Edelbrock carb.
                                     
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                                    • pishta

                                      pishta I know I'm right....

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                                      boils out of a carter on a cast iron intake. Every morning my electric carter pump would run load free for about 4-5 seconds. If I tried to start it without the pump on it would run for about 5 seconds and then sputter and die. Fuel was going somewhere and on a carter it can only evaporate. My Nikki 2bbl with clear sight glass will hold fuel for about a week at the level mark. The facet style 'jiggler' electric pump fills it and there is a tap with a check valve that sends the fuel back when the bowl is full. Todays fuel will evaporate and leave a white jello like crap. Lawnmowers are notorious for getting their bottom bowl jets clogged with this crap.
                                       
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                                      • toolmanmike

                                        toolmanmike Moderator Staff Member FABO Gold Member

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                                        Exactly, put some E-10 in a quart jar and watch how fast it disappears. Some 2 barrel carbs have bowl vent's that are sealed until the throttle is opened. Those aren't as effected by evaporation. A cast carb on a iron manifold that is at 200° with ethanol inside that boils at 155° and here lies the problem.
                                         
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                                        • Dana

                                          Dana FABO Vendor FABO Vendor

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                                          Today’s pump fuel is approximately 50% vapor @ 170*F.
                                           
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                                          • royslead

                                            royslead Well-Known Member

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                                            Just because you can't see something, doesn't mean it does not exist, or is impossible. You can't really SEE the air you breath in, right? The Tooth Fairy is real! ...and I don't care WHAT you say!
                                             
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                                            • Dana

                                              Dana FABO Vendor FABO Vendor

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                                              With 180* or 190* T-stat, when you shut down and walk in the house, she will spike to around 210* -215*F. Anyone with a carter who thinks they have it bad, should see the tiny fuel capacity of a Quadrajet. Especially the early Quadrajet.
                                               
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                                              • 66fyssh

                                                66fyssh Don't Stop Believin' FABO Gold Member

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                                                ...and poof, the fuel is gone in no time.
                                                 
                                              • pishta

                                                pishta I know I'm right....

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                                                exhale in 20F weather.....:rolleyes:
                                                 
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