plug reading help?
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plug reading help?

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    Senior Member californiadreamin's Avatar
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    Default plug reading help?

    Hey guys, im hoping somebody could help me make some sense of this. I have an olds in my river boat, 10:1 compression, iron heads
    and an 850 dp. I run shell or chevron 91. Plugs have always been white. I keep jetting it up with no color change. The plugs read the
    same with 80s in it as they do with 95s in it. Thanks for any insight

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    if plugs have always been white and you havent had any problems then dont change or stress over it. may just be a HOT plug that Olds and/or the boat manufacturer chose to run in that engine. how long are you running the engine before checking the plugs??

  4. #3
    gn7
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    Quote Originally Posted by californiadreamin View Post
    Hey guys, im hoping somebody could help me make some sense of this. I have an olds in my river boat, 10:1 compression, iron heads
    and an 850 dp. I run shell or chevron 91. Plugs have always been white. I keep jetting it up with no color change. The plugs read the
    same with 80s in it as they do with 95s in it. Thanks for any insight
    The color of the ceramic has nothing to do with the AF. By the time you have colored the ceramic of a plug in a boat, you're dead rich. Some people read the edge of the steel shell, I perfer to read the color ring at the base of the ceramic. Don't even bother if you don't have a plug scope, you're wasting you time.
    The part of the ceramic you are looking at has more to do with the plugs heat range and whether its a standard tip or extended tip plug. Extended tips plugs run pretty damn white.

    Without knowing the carb size and type and manifold type, giving us the jets size is meaningless.


    The color of the ring at the base of the ceramic is all you are concerned with, not the whole thing. If you don't have a plug scope, never mind.

    Click image for larger version. 

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    Or you can use method 2 and look at the color of the edge of the shell. Neither of these mean jack shit if you drive it around part throttle or idle it before reading the plug. It only means something if you run it flat out for a distance ON A NEW PLUG and chop the throttle and pull the plugs. Other wise you are guessing.





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    Senior Member californiadreamin's Avatar
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    Thanks guys, gn7 maybe i wasnt clear in my first post, its a holley 850 double plumper, 4781-2. Problem is I ran it a couple seasons and melted the #6 piston. They are hyperuetectics and after the rebuild I just want to make sure I am doing what I can to keep it happy. I supose they are fairly hot plugs, ill post a couple pictures this afternoon. I don't run it wide open very long or very often. I'll run it at cruise for about twenty minutes then check plugs. I wanted to get an idea of a/f at cruise conditions where it normally runs before the power valves are wide open. I just want to get an idea of cruise conditions then move on to wide open throttle checks. Thanks again

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    Senior Member californiadreamin's Avatar
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    Sorry intake manifold is an edelbrock performer dual plane

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    Senior Member EVILFORCE's Avatar
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    What Uncle Bob said. If you don't have him on ignore. He is a ornery old coot.

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