Enlighten me about spark plugs

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    Replies: 43
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    quote Pappy:

    Let me simplify this for you although with a simple Google search you could have avoided printing the mis-information yourself.
    http://matchlessclueless.com/mechanical … mperature/

    Secondly, give us an example on an outboard where the intake is closely couple to or an integral part of the exhaust. Most I have seen have the intake on one side of the cylinder and the exhaust on the other.

    The point here is that folks are here to learn FACTS about their outboards. If you know something as FACT, fine, post away. If not, bear in mind that you are possibly misleading those who are here to learn and worse yet, cost someone money and time following that misinformation.

    Talking to me here..?


    US Member - 2 Years
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    Replies: 43
    Topics: 20
    quote Pappy:

    Nice, thanks for the link. Gonna give it a thorough read-thru


    Replies: 389
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    quote thepetrolist:

    Ah, I see!
    Thanks for the clarification.

    Today I once again bought some new plugs. Luckily I work at an auto supply store so I can check up on plugs while at work. 😀
    We were out of NGK B7S and Champion J4C’s but I got Denso W22S-U:s . They matched the specs so I thought I’d give it a shot. Installed them, pulled the starter.. And off they went! Ran better than ever before, both the HD and the Sportwin. Which brings me back to the thought about the Bosch W8EC plugs being dodgy. But what is the chance that FOUR brand new plugs are bad?

    The chance of four brand-new spark plugs – made by two entirely different manufacturers – being ‘bad’ out of the box is pretty slim. Of course, in a two-cylinder motor, all it takes is +one+ bad plug to make things go awry.

    quote :

    Any other thoughts?

    All I can tell you is that there most certainly +is+ an answer, and with the proper knowledge and instruments, it could more than likely be found. But I sure as heck can’t tell you, not from where I sit, way out here in the cheap seats.. 😉

    And again, I’ve simply had crap luck with both Bosch and Champion, in all but a few previously-described situations. All plugs pretty much look & feel alike, but there’s some very serious and subtle science going on in those things.. a wide-world of trade secrets, I’d wager.


    US Member - 1 Year
    Replies: 214
    Topics: 25

    I’ll try to explain what happens if you use plugs that are too hot. I have experienced this on two motors.
    At full speed the plugs get to hot and the mixture pre-ignites resulting in a drop of rpm to a much lower speed. Then
    since there is less heat the plug cools off and the motor starts running faster. On a 3.5 Chrysler air cooled motor it cycled over and over.
    On a Johnson A-50 the cycles were less clear but it did not run well.

    On the Chrysler I had inadvertently installed a H10C instead of the correct H8C.
    On the A-50 I was simply experimenting. I tried D9s, D14s, D16s and D21s.
    Ended up using D16s.

    John Schubert

    Lifetime Member
    Replies: 75
    Topics: 5

    Scott, very true. Using the recommended plug should work every time unless there are any of the other issues evxident. I will make one additional comment, the newer Champion plugs with the siffix "C" for copper, don’t work nearly as well as the ones with the suffix "J". I found that the NGK plugs recommended for replacement of the J 6 J work very well.


    Lifetime Member
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    In the "good old daze" of sloppy sand castings, loose tolerances, and poorly refined fuels & lubricants, the recommended spark plug was only a sugestion. Some of our apposed cylinder antiques ran best with a different heat range plug in one cylinder. Many were damaged by over advancing the magneto. Things improved with better aluminum alloys and the uniformity of die casting. Even so, some of the Johnson "HD" and "TD" models had vapor lock problems in hot weather. The third port on these mounts the carburetor right next to the exhaust manifold.

    The designated "J" Champion sparkplug had the side electrode end over the center of the center electrode. This was said to give a more "open" spark for better ignition in two cycle engines. I always file my new plugs back like that. I figure it can’t hurt. For one thing the way electrons gather on a flat surface makes it easier to jump from a sharp edge. For another thing, the edge gets hotter and wears down faster. A worn sparkplug will always have rounded edges. A little filing there can extend it’s life.

    . . . . . 😉


    US Member - 1 Year
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    You're only as smart as the person you're talking to.


    Canada Member - 1 Year
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    I too love to collect nice original plugs Tubs.

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