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  1. 10-17-2018, 04:26 PM #1
    mikesxpress
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    250 CMS Pro XS V8 spark plug check

    9.7 hours
    Wanted to pull the plugs and do a check on carbon build and gap. Some carbon as expected but the gap on all 8 plugs were off. Supposed to be .035. I do all my plugs with a wire and I found the factory had them ranging from .032-.033. Wire brushed, shot of brake cleaner, dab of anti-seize on the threads, dab of dialectical grease on the end, and back in.

    Tip: The boots go waaay up in there and were a PIA to take off the 1st time. Spray the entire boot with 303 protectant and it makes it much easier to R&R the boots and you can feel them seat on the plug.

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  2. EuropeanAM
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    Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #2 10-17-2018, 05:00 PM
    Please be sure to reference your Engine Serial Number when posting. Thanks!

    Glad to hear they were at least within .003"...


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  3. mikesxpress
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    #3 10-18-2018, 11:44 AM
    Serial# 2B529759

    Don would you install a set of plugs at .003 off?
    Me either....
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  4. Hickory Legend
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    #4 10-21-2018, 10:18 PM
    Wouldn’t it be better to be off on the short side so as it wears, it’s closer to .035 than wearing wider?
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  5. mikesxpress
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    #5 10-22-2018, 05:08 AM
    The engine was designed to run correctly with 8 plugs set to .035. Your not going to realize optimum performance unless they are set to specifications.
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  6. EuropeanAM
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    #6 10-23-2018, 03:05 PM
    Quote Originally Posted by mikesxpress View Post
    Serial# 2B529759

    Don would you install a set of plugs at .003 off?
    Me either....
    Nope- sure wouldn't. That's actually a LOT closer than most of the previous model's gaps I checked, though.


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 47 years (learn something new every day).
    Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor
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