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  1. #1
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    Opti spark plugs are black

    I just finished year two with my 200XS ROS. Great motor. Year one, break in and maybe another hour, the plugs came out black. Year two, ran a few tanks of gas through it, plugs came out black when I pulled them to fog the motor.

    Is this normal?
    Attached Thumbnails Attached Thumbnails Oct 2019 plug.jpg  

  2. #2
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    Hi David - let' start with the plug # just to be certain of the correct plug - my Parts Manual revised 2017 version shows an NGK 1ZFR7M . but I believe a discussion on here was that a supplement for gen 2 showed a 1zfr5g was correct - the 5 is supposed to be 2 ranges hotter . I can only confirm what my revised parts manual shows - 7m.
    On the Service Manual of February 2001 so it' gen 1 shows NGK -PZFR5F-11 . Heavy Duty - gapped at 40 So this is all the info I have available other than calling merc tech , but i suspect the call should be made to ascertain the correct info on the subject.
    I did not recieve a supplement with my ServiceManual . So there may be more to the story and the thread on here may be correct - but sometimes things get mixed up in translation and it got crossed up . Remember my pats manual is up to date but a supplement may still Trump that . Doubtful though since it' 2017 . Let' see if we can stir a Master Tech up for an answer-
    Last edited by kellytheaker; 10-25-2019 at 10:28 PM. Reason: Correcting

  3. #3
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    How many hours on engine? When I had a 300XS I had the injectors(fuel/air) cleaned at about 180hrs because plugs were way blacker than yours. Also had some buildup on top of pistons. But overall if it runs good be happy!
    Checkmate 2002 Convincor 270 496 MAG-HO

    2003 Cougar 22MTR w/300xs SOLD
    90 21Skater w/300xs - sold
    98 STV Euroski w/280 - sold


    2006 Trailblazer SS 6.0l 395hp

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  5. #4
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    David , had mine on a stand and pulled a plug for your reference and was 7M . Burn on #2 showed dark brown visual on open side and carbon dark on rest of plug surround . Rememer this would have been an idle , cool run into dock . This plug #2 was as expected - i thought anyway - when I fog I will have a more consistent finding for you to compare to . So anyonr have this supplement to the manual Stating different plug ?

  6. #5
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    Should get injectors serviced as well. I get mine done before every season and a few of the air injectors are caked with carbon build up

  7. #6
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    Maybe 20 hours on the engine

  8. #7
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    David - I went to fog the motor and only got 1 bank of plugs done and all looking similar , ceramic is a nice dark brown in phases it seems . White areas then back to a dkbrown in a pattern **** the darkest at back of elective opening . I will be certain of the other bank tomorrow - when I get another can to finish up . You didn' by chance introduce a break in again - delivering an oil rich delivery? Or I suspect you putted around a bunch before putting away last run since it' a tad chilly . You have not stated the plug but suspect 7m

  9. #8
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    When I had my 300xs, was told not to fog the engine because could foul the injectors. not sure if it's changed?
    Checkmate 2002 Convincor 270 496 MAG-HO

    2003 Cougar 22MTR w/300xs SOLD
    90 21Skater w/300xs - sold
    98 STV Euroski w/280 - sold


    2006 Trailblazer SS 6.0l 395hp

  10. #9
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    I thought it was a good thing for the bore and rings ,but now you got me thinking . Can anyone else confirm this statement . Thanks for bringing that forward .

  11. #10
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    Dark plugs are normal for an opti on 91. They only run 90-110psi compression for an average. Lots of soot and carbon from running water cooled fuel into 110 compression.
    Try to find a low rvp fuel as standard v-grade and a-grade is close to 10rvp look for 8 or less. I’ve been splashing vp4sse to cut rvp
    Ohm the plug from end to tip if only a small spot is 5000 ohm they’re do for a clean or replacement.

    Honestly were here supposed to replace the crush rings each time you pull it out to see them.

    I find more broken in the nut then fouled. But a batch of weak 91 can black them um good

    Run some pea type cleaner to keep them clean.

    As for fogging i dont think it hurts. But merc doesn’t recommend it. They squirt dfi in the spark hole and manualy rotate the engine to oil the rings and bore. I use a spray bottle myself just for a finer mist.
    Last edited by Motv18; 10-27-2019 at 09:46 PM.

  12. #11
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    My mechanic says don't worry. Idles well, runs hard at top end, relax

  13. #12
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    That is a normal plug for an Opti. Remember it is a 2 stroke. The tip is brown = good burn.

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