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  1. #1
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    Dec 2017
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    FYI/BCB/Mercury 4s

    FYI if you haven’t pulled your spark plugs the gap will probably be way off. Pulled mine yesterday to clean at 74 hrs 2021 Caracal 225 4s all were in good shape. Motor ran as should but I’m sure some performance was lost. Here are my readings:

    This is not an isolated issue. I know of several Mercury 4s owners with factory installed plugs with gap inconsistencies.
    Spend the $100 and get a Mercury Service Manual from Mercury publications. Every aspect of your motor is in there it’s an invaluable tool.

  2. #2
    Great Info my friend, many thanks
    Mike
    2022 Basscat Jaquar
    Mercury 300 Pro Xs

  3. Member
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    #3
    Yes, very good information.

  4. Member
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    Apr 2020
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    Alexandria, La.
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    #4
    I lost performance within a year and under 50 hours. I pulled the plugs are they looked terrible. Gaps were all over the place. I gapped the new ones and the engine is running great.
    2021 BassCatt Pantera II
    200 Pro XS(3B056653)
    Motorguide Tour Pro

  5. Member
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    Jun 2013
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    Batavia, Ohio
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    #5
    I also had an issue with the factory plugs in my 300 on the lynx. I found one was fouled out. So I went ahead and replaced all eight and gapped accordingly. Motor has been good since.
    Gun Control..... Is hitting your target every time

  6. Member 06 SB's Avatar
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    Feb 2012
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    West Point Lake, GA
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    #6
    Don is doing my annual maintenance again this year. No worries for lucky me.

    USN Retired
    2020 Basscat Caracal
    2020 Mercury 225 ProXS 4s



  7. Member
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    #7
    Quote Originally Posted by 06 SB View Post
    Don is doing my annual maintenance again this year. No worries for lucky me.
    Mine will only go back to Sherm if it needs a G3 diagnostic check for any issues I can’t fix. Sherm is an outstanding Cat dealer and mechanic with all the updated Mercury certifications. Highly recommended him for a Cat purchase.

  8. Member
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    Apr 2014
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    SW, Ohio
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    #8
    so gap was wrong when new? gaps don't decrease with use??
    2022 z519 cup 225 merc 4s ser # 3B210484. 2--hds12 live units. 2 poles, atlas plate, ghost, hamby's, active target, merc digital gauges
    2002 basscat pantera 3 (dad bought new) sold 8-2-22
    2000 stratos 20 ss (bought new) 200 hp Rude ficht great boat/motor sold 11-21
    pulled by a 2500HD Denali
    proud dad of an ARMY Captain
    MAGA
    ASE/GM Master tech before tools

  9. Member
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    #9
    Quote Originally Posted by mactlman View Post
    so gap was wrong when new? gaps don't decrease with use??
    Maybe change some from use but, minimal .001 or .002 at most. Mercury buys these pre gapped from a vendor I believe from Mexico. Apparently they don’t check before installation at the factory.