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Harley Davidson WL spark plugs gets black

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  • Harley Davidson WL spark plugs gets black

    Hi, today I did a complete check in my motorcycle to verify the reason of the backfire through the carburetor.

    After a long check, I realized that the iridium spark plugs were just black.

    At first I thought that the backfired should be caused by a lean mixture, so I have closed the low speed needle clockwise and turned back three clicks up....but then if the spark plugs are black, this means that the mixture was too rich?

    I am puzzled...any help?

    What I did was to replace the spark plugs and tun the low speed needle to three clicks up, nothing else. Now the motorcycle starts easy and there are no flames any more.

    Anyone could help me to understand what happened and what should I do?

    Thank you!

    Ed
    Attached Files

  • #2
    Good luck running those plugs.They are made for finely controlled fuel injection.NOT linkert & not an engine that lets oil in.As Cotton always says..check for intake leaks & I will add:read up on how to adjust carb.

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    • #3
      Originally posted by duffeycycles View Post
      Good luck running those plugs.They are made for finely controlled fuel injection.NOT linkert & not an engine that lets oil in.As Cotton always says..check for intake leaks & I will add:read up on how to adjust carb.
      PS: Beware of many modern NGKs, too.

      (Unless you have a modern ignition, you do not want a resistor plug.)

      ....Cotten
      PS: Even if they say it ain't.
      Last edited by T. Cotten; 03-01-2019, 01:51 PM.
      AMCA #776
      Dumpster Diver's Motto: Seek,... and Ye Shall Find!

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      • #4
        I think that most antique motorcycles are allergic to iridium.

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        • #5
          Originally posted by HDSmitty View Post
          I think that most antique motorcycles are allergic to iridium.
          I read somewhere it killed the dinosaurs, Smitty!

          So it makes sense.

          But I think most plugs foul because of a poor mixture.

          Worn carbs can't tune high and low speeds the same,
          and if there's a vacuum leak, it won't run any way but 'fat'.

          ....Cotten
          PS: Ed!
          It looks like too many threads on your plug, too.
          Last edited by T. Cotten; 03-08-2019, 11:30 AM.
          AMCA #776
          Dumpster Diver's Motto: Seek,... and Ye Shall Find!

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          • #6
            Weak spark in that cylinder maybe ?

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            • #7
              Originally posted by Paps View Post
              Weak spark in that cylinder maybe ?
              Always a possibility, Pa..

              Coils and wires can be fickle, especially repops.

              But cylinders burning different brings back up evil manifold leaks;
              So we bubble-test to get that variable out of the way.

              Testing coils qualitatively might be within my grasp, but not quantitatively.
              (I remember spinning my Edison-Spltidorf with a wire wheel, and the leaky wires made lightning between them.)

              ...Cotten
              Last edited by T. Cotten; 03-08-2019, 05:45 PM.
              AMCA #776
              Dumpster Diver's Motto: Seek,... and Ye Shall Find!

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