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  1. #1

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    Spark Plug Gap with Higher Boost

    When you run higher boost above 15 psi, you might want to re-gap your spark plugs to a smaller size. Higher boosted Yamahas with higher boost applications *(15+ psi) you will want to gap your spark plugs 0.018" - 0.022".
    The rule of thumb is decrease your spark plug gap by 0.005" increments at a time until the desired stable rpm gap is reached or the surging caused by a high speed miss is gone. There might even be a need to go one heat range cooler. With NGK # 6 plug is hotter then a # 7 plug. These are things that can be done to fine tune your engine. (even plug indexing)

    Take Care
    C J
    Last edited by cjk6119; 12-04-2019 at 06:41 AM. Reason: TYPO

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  3. #2
    battsy's Avatar
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    Interesting. Question so I have a 2016 fx svho stage 2 from Dean. I dont know what boost numbers I am running but from what I have researched here stock is around 11-13psi? I also think stock gap is .035 so you think I should regap down to .018-.022?

  4. #3

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    To Bastty. The gap Bastty you have is fine. I just realized my typo, it is when the boost levels are over 15 psi. I miss read my own post.

    Thank You Battsy
    Take Care
    C J
    Last edited by cjk6119; 12-03-2019 at 02:19 PM.

  5. #4

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    One other thing would be good, is a little bit of copper lube ( anti seize ) on the spark plug threads. That will avoid a chance of breaking off the threads of a spark plug in the head. Do not use too much or it can change the heat range of the plug, the threads has to have good contact with the head in order to help dissipate heat out of the spark plug..

    Hope you all find this a help.
    C J

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  7. #5

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    I’ve never messed with the gap, but on my SHO I run the colder SVHO plugs. I check the gap before installing my plugs, but I’ve never adjusted them past factory specs and always had great performance from my skis.

  8. #6

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    Quote Originally Posted by Shortbus_FZS View Post
    Iíve never messed with the gap, but on my SHO I run the colder SVHO plugs. I check the gap before installing my plugs, but Iíve never adjusted them past factory specs and always had great performance from my skis.
    For you and I the stock gap should be fine. There is a need for adjustments when these guys are running boost levels 24psi 26psi 30psi or even 40psi. Don`t forget some rpm levels are 9,200 or 9,800 better.

    C J

  9. #7
    abracadabra's Avatar
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    I’m running the gap at 16 thousands.

    30 LBS Boost @ 9850 rpms on E85...


  10. #8
    .018 27 psi at 9800rpms SC E85
    Last edited by FXSlowKroozer; 12-05-2019 at 03:48 PM.

  11. #9

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    when you change the original gap on a sparkplug say from .038 (out of the box specification) to say .020 (desired plug gap) once the sparkplug has been run and heated and cooled several times the gap will tend to try to go back to it's original manufactured setting some what. It is a good idea to re check your plug gap from time to time to ensure maximum performance from your engine.

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  13. #10

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    Here is another fine tuning trick you can do to your plugs is what's
    commonly called "side gapping" them. This is when you
    take a small file to the ground strap and
    cut it back so it only covers about half of the center electrode.
    This exposes the spark to the open cylinder and combustion
    area more and prevents the shrouding that the full length ground strap tends to do if left unchanged.

    Hope this of some help.
    C J

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