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  1. #1
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    1999 200 Opti - What is this spark plug trying to tell me?

    Doing some preventive maintenance on my 1999 200 Optimax (ser. #0G886121), and pulled the plugs. Every plug looked exactly the same except for the one that came out of the #6 cylinder. In the attached photo, the plug on top is how #1 - #5 looked, and then my #6 is the one on the bottom (which is much more black and sooty looking). Anything to be concerned about??? The motor seems to run ok. I was doing this preventive maintenance work because it stumbled on me coming out of the hole the other day, and I just wanted to replace all the basic stuff. Thanks in advance for any ideas.
    IMG_4653 (1).jpeg
    Last edited by JCJ; 07-13-2019 at 03:58 PM.

  2. Member lpugh's Avatar
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    #2
    compression test is in order
    Thank You Leon Pugh

  3. Member
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    #3
    and spark test.



  4. Member Ranger519VS's Avatar
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    #4
    Check reed valves while you are at it
    Butch Derickson
    2011 Z521 w/250 hp SHO
    Traverse City, Michigan

  5. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #5
    If you had been idling, that's not extremely abnormal. Lowest cylinder will often get the "excess" fuel from the system (as well as the most oil).

    Plugs are regular ANNUAL Maintenance Item... be sure to check the plug wires while you are at it.


    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

  6. Member
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    #6
    Thanks Don. I know you don't know me, but I've viewed your feedback several times over on this forum and realize you know your stuff. I was hoping you'd respond . While I got you , I do have another question related to this. While reading about the stainless reed valve issues that are prone to breaking on these motors, I pulled the intake to inspect them, and found one chipped. It was on the #4 cylinder though which is not where this plug was. Even though that was the case, could that have anything to do with this #6 plug looking like this? Also should I be concerned with the chipped part of the reed being off in the motor somewhere, or would it have told me it was there already? Thanks again.

  7. Member lpugh's Avatar
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    #7
    The number 6 is what got my attention!
    Compression test should be the first thing, Don probaly noticed that it was allready recomended. It is the ablosute pits to invest time and money, then find out you have a compression problem or you have pulled it apart and have to put it back together to do the test. For sure should have been done before reed inspection
    Not taking anything away from Don, he knows far more than I do about Mercurys, he may very well be the best Mercury Tech in the nation
    Thank You Leon Pugh

  8. Member
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    #8
    I hear ya, and probably should have done that. However, I'm to far in it now. This started out as just going to complete some routine maintenance, and change out my fuel lines/bulb due to some sputtering I started getting when trying to take off. While reading about symptoms of bad reeds though, it sounded very similar to what I was experiencing so I decided to go ahead and inspect mine (which is how I found the chipped one). Now that I know this, I'm going to go ahead and replace them to make sure I they're right. When I get it back together, I'll complete the compression check, and cross my fingers . Hopefully it all checks out well. Thanks for taking the time to respond, and the advice. Appreciate it!

  9. Member
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    #9
    Couldn't you still do a compression check? Wouldn't be accurate but would indicate if one cylinder was down on compression compared to the others.On the reed situation...mine had a chip,never found it in the motor,must have passed through,no damage.Replaced them with Carson reeds.Have seen and heard of others that did catastrophic damage.

  10. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #10
    Due diligence would be in order- a compression test at a minimum, and inspect as best you can for the remains of that reed.

    It "sounds" like you may have been lucky and it passed through.

    Reed wise, I recommend (and sell) TDR Reeds. See Rhonda's post (pinned at the top of the forum) for contact info.


    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