exhaust backfire

Big Block A body Tech

  1. yellow rose

    yellow rose Overnight Sensation FABO Gold Member

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    You have enough ignition that the plugs should not have any color on the porcelain. If there is color there, it’s rich at idle, and I’d probably say pig rich.
     
  2. George Jets

    George Jets 1967 Dart 2 Door FABO Gold Member

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    A quick swap in of a points distributor is a simple test. Then if it runs better without backfiring, he will know his problem is in the ignition system. Then he can repair or replace it as he sees fit.

    Simple process of elimination, ultimately it's @Jbarker that is going to find what the problem is. We are just trying to lead him to discover it by giving him a few options to try.

    Yes, pictures of all of the spark plugs in order as they came out is a great idea. The pros on here can read how they are burning, and can relay the info of where any problems are.

    Screenshot_20210402-152341_Gallery.jpg
     
  3. George Jets

    George Jets 1967 Dart 2 Door FABO Gold Member

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    Yes, pig rich at idle gives the opportunity for fuel to enter the exhaust system during the open valves at overlap during idle from the big cam that is in there.

    Now all you need is a misfire spark to set it all off and Bang, there's your Backfire again.
     
  4. 512Stroker

    512Stroker We are all here because we are not all there.

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    Im lost, the OP is triggering a Hyfire box with a points distributor?
    If so, that dont sound right in any world.
     
  5. George Jets

    George Jets 1967 Dart 2 Door FABO Gold Member

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    No, the points distributor can be used all by itself with a standard coil as a test to get it to run without backfiring.

    An old 60s 70s thing, one hot wire and you are running. (as you probably know).

    He has a spare points distributor to use for the test.
     
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    • George Jets

      George Jets 1967 Dart 2 Door FABO Gold Member

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      The owner @Jbarker is going to strike gold here pretty soon and get this Backfire problem figured out.
       
    • Jbarker

      Jbarker Active Member

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      Thanks for the vote of confidence!
       
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      • inertia

        inertia Well-Known Member

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        And oxygen.

        I used to weld used gas tanks after running an exhaust hose into the tank to perge oxygen and flammable vapors .
         
        Last edited: Apr 5, 2021
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        • Jbarker

          Jbarker Active Member

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          Impossible.... or so I thought. I changed the carb and the problem was still there!
          With the first carb (Holley hp 850), I leaned out all 4 corners until it would barely run, but it didn’t help. So I switched carbs and the same problem was there. But... I never took the time to really lean out the idle screws on the new carb. I did so yesterday and the problem seems to be gone. I am only cautiously optimistic, because the problem has always seemed worse in hot weather and it is cold today here in Buffalo today. But if my memory serves me correctly, even last fall it would still backfire on cool days at least a little bit. I had no backfires today! I need to get it out and drive it some more to be sure it’s good, but first I need to get it inspected. Thanks so much to all of you who gave your expert insight and advice. I think I am back in action again!
          -Jay
           
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          • yellow rose

            yellow rose Overnight Sensation FABO Gold Member

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            Thats why we asked for pictures of your plugs.
             
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            • RustyRatRod

              RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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              DUHHHHHHH.jpg
               
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              • Ceedawg

                Ceedawg Well-Known Member

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                • MOPARMAGA

                  MOPARMAGA FABO Gold Member FABO Gold Member

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                  My old charger would load up & backfire, from unburned fuel in the exhaust.
                  I'm thinking those 2 inch pipes are causing not enough exhaust gas velocity to get the exhaust out of the pipes while it's idling.
                   
                • Ceedawg

                  Ceedawg Well-Known Member

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                  Get car-truck up to speed and turn off ignition, coast, pump gas then turn on the key, POW, big back fire. Sometimes muffler came off. Do it when a bunch of people are walking down the street and they jump like a bomb went off.
                   
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