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Thread: Harley Davidson WL spark plugs gets black

  1. #1
    Join Date
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    Default 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
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  2. #2
    Join Date
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    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.

  3. #3
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    Quote 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 at 02:51 PM.
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  4. #4
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    I think that most antique motorcycles are allergic to iridium.

  5. #5
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    Quote 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 at 12:30 PM.
    AMCA #776
    Dumpster Diver's Motto: Seek,... and Ye Shall Find!

  6. #6
    Join Date
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    Weak spark in that cylinder maybe ?

  7. #7
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    Quote 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 at 06:45 PM.
    AMCA #776
    Dumpster Diver's Motto: Seek,... and Ye Shall Find!

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