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  1. #1
    2 x SLT750 & Learning skoots's Avatar
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    Confused - One plug oil-fouled

    A little history on my skis...I thought I lucked out when I picked up what seemed to be an excellent deal last month, two SLT 750s and a double trailer for 2K. The skis had 150 hours on them and the couple I bought them from had not used them for the past 2 years. From what I could tell, everything on them is stock and not a single bolt has seen the likes of a wrench. The guy told me one ski runs fine and the other makes an awful noise when starting. The first thing I did was dump the old oil and gas in both of them and hit the water with the working one. I've got 15 hours on it so far and it runs great.

    The problem with the second ski turned out to be a slipping starter drive. After changing it, I went for a test ride only to have the exhaust manifold gasket spring a leak on cylinder #3. Thanks to the great information spoon fed to me by members of this forum, I got that fixed as well and installed brand new plugs gapped at .028

    Now the ski seems to be in limp mode and won't go past 25. I pulled the plugs and what's strange is that #3, which I had sprayed fogging oil after the gasket leak, and #2 are clean and dry, but #1 is oil-fouled. When I sprung the gasket leak, #1 plug was nice and clean so I'm wondering why it's fouling all of a sudden.

    I've done lots of reading on here and know there are many upgrades I should probably do, such as change the pump and so on. But I'm on a budget and trying to identify this one problem for upcoming vacations. The other ski worked like new right off the bat and both have similar histories.

    So my question is, how do I go about identifying this one problem without spending a fortune changing everything. Where should I start?


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    How many minutes has the engine run since you fixed the water leak problem?

    Could this just be excess fogging oil in the crankcase, that isn't getting burned off because the RPM has yet to get up high enough to force the oil up and out?

    Have you tried running it on the water since you cleaned that fouled spark plug?

    If any one cylinder isn't producing power, you will loose a LOT of RPM.

    Any warning messages on the MFD, or a red light?

  3. #3
    Plugs foul all the time. I would burn off the plug (or just use a new one) and take it out again. According to what you said, the boat sat for ~2 years so maybe something just got gummed up or oil build up. If it ran fine otherwise I wouldn't be worried. Now, if you fouls a plug again, then look deeper.

    Edit: How is the compression on #1?

  4. #4
    2 x SLT750 & Learning skoots's Avatar
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    Thanks guys,With the stories I read around here, I'm so paranoid of burning an engine that I only ran it 2 maybe 5 minutes max and brought her back home. Your comments are reassuring though.I can confirm that it's not a fuel pump issue. Just changed the fuel filter, started it and the filter filled right up.

  5. #5
    2 x SLT750 & Learning skoots's Avatar
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    Here is something I just noticed reving it on the trailer. Cylinders 1&2 get hot, but #3, the one that took in water stays cold. Time to find a compression guage?

  6. #6
    Check to see how the spark is on that cylinder. It could be very weak and thus, not creating a good burn. You might have to shorten the plug wire. Check the compression on all cylinders and get back to us.

  7. #7
    If the cylinder has compression then it could be a stuck needle and seat if it has sat for 2 years

  8. #8
    2 x SLT750 & Learning skoots's Avatar
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    OK I've got a spot even compression of 120 on all cylinders. The plug seems to fire, although I should mention that I installed brand new NGK Iridium plugs which are the needle type and I'm not familiar with the spark they should be giving off. I also installed Iridium plugs on the other ski and it runs fine. In fact I couldn't believe how much more responsive it is with these plugs compared to regular ones.

    Any ideas? Could it be a carb issue?

  9. #9
    2 x SLT750 & Learning skoots's Avatar
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    Quote Originally Posted by prochamp View Post
    If the cylinder has compression then it could be a stuck needle and seat if it has sat for 2 years
    Yeah, it sat outside under a tarp for 2 scorching hot summers and freezing (-40) cold winters

    Can I get to the carbs without pulling the motor?
    Last edited by skoots; 07-25-2008 at 11:49 AM.

  10. #10
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by skoots View Post
    ...Can I get to the carbs without pulling the motor?
    Yes.
    The Service Manual outlines the procedure.

    Quote Originally Posted by SantaCruz163 View Post
    ..You might have to shorten the plug wire...
    Unscrew the spark plug cap from the wire, then trim about 1/4 inch from the wire, then reattached the plug cap.

    Often the very end of the wire gets frayed inside, and doesn't conduct very well. The cap has a pin that presses inside the center of the wire.

    Might want to do that on all three plug wires (six if you do both skis).

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