Time to de-carb my 2-stroke Johnson?

Discussion in 'Outboard Maintenance' started by cslascro, May 18, 2012.

  1. cslascro

    cslascro I Love microskiff.com!

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    After using the boat on a very short trip last night (about 30 minutes of running on plane with very little idling), I found this this morning. It smells like engine exhaust (i.e., carbon). I'm thinking last night's running helped push this out the vent hole.

    I've been idling this engine a lot due to using the boat in a river that is all "No Wake." Last weekend, we did a three day trip on the St. Johns that was primarily just going slow so the wife could take photos.

    Of the last 25 hours on this engine, I'd venture so say that at least 23 of those have been under 2500 RPM.

    I also had to use some Wally-world 2-stroke oil in a pinch last weekend (about a quart)--previously I had been using Penzoil Marine and Quiksilver.

    The lower unit lube is clean and fine. My diagnosis for this is carbon buildup in the engine's exhaust. I'm planning on doing the Seafoam treatment.

    Thoughts?
     
  2. Brett

    Brett > PRO STAFF <

    Carbed 2 stroke outboards are extremely inefficient at low rpms.
    Up to 40% of the fuel oil mix entering the cyclinders is blown out the exhaust unburnt.
    Take the boat someplace without any No-Wake zones and let her rip!

    [smiley=carcrash.gif]
     

  3. cslascro

    cslascro I Love microskiff.com!

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    Good advice, Brett!

    Here's a link to the photo. Let me know if any of you all think this is more serious than my diagnosis.

    http://www.flickr.com/photos/59745094@N07/7223217022/
     
  4. Brett

    Brett > PRO STAFF <

    [​IMG]


    Normal discharge for a 2 stroke run at low rpm's for extended length of time.
    Unburnt fuel/oil mixed with burnt fuel/oil to make a thick dark mess that coats
    the interior of the exhaust housing (mid-section), then trickles down later and out water relief holes.
     
  5. Creek Runner

    Creek Runner Well-Known Member

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    Just an OMC doing it's thing, like brett said go run it wot for aobut an hour. If you want and some Yamaha Ring free to the fuel.
     
  6. cslascro

    cslascro I Love microskiff.com!

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    Sounds good guys!

    "Just an OMC doing it's thing."--I love it!

    It cracks me up when I go to buy parts for this motor and see that 1984-up take the same parts.

    It's loud and smoky, but it does the job.

    Thanks again!
     
  7. jgregory01

    jgregory01 I Love microskiff.com!

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    I have a 1999 Johnson 50hp 2st J50pleea. I found the same thing once. Its hard for me to tell from your pics but I think you had the same thing as me.

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    Brett helped and explained that it is unburnt oil. Strokers arent pretty but they get the job done. I have had no problems related to oil or anything. You are find I would suspect.

    Are you running on a remote oil setup or do you pre-mix? I was remote but premix now. Might be my imagination but I think it runs a little better, and I dont have this problem anymore. Just a thought.
     
  8. cslascro

    cslascro I Love microskiff.com!

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    I pre-mix.

    The oil brand switch I did in the last full tank may have contributed, and I've really been spending a lot of time running the motor at low RPMs. As I've researched this issue, I'm finding many people who use a small 2stroke as a kicker for trolling have the same issue (lake fisherman).