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  1. #1

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    black spark plug

    Ok I had just bought this ski and hydro locked it. The back piston was crack so I replaced it along with rings. I ran it Saturday for an hour and ran fine. I took it out tonight and that spark plug is black, dried black. I could use some help. I also ditched the auto cock yesterday. Here is a picture of the plug.


  2. #2
    ujustlost's Avatar
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    What year and model ski you have? Chances are you need 8's on the plugs and your running 7's Don't think that's your entire problem but that's where I would start. Mike

  3. #3
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Quote Originally Posted by ujustlost View Post
    What year and model ski you have? Chances are you need 8's on the plugs and your running 7's Don't think that's your entire problem but that's where I would start. Mike
    I'm going to agree with this ^^^^^^

    Also may need to add some more fuel to the mix via the carb adjustment screws.

  4. #4

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    Sorry guys the ski is a 94 SL 750. I am running 7BRES plugs. Does plug actually look lean? I thought a white plug was lean. I wanted to rebuild the carbs, but when I opened them up all the screws inside are seized. If I could get them apart I would have rebuilt them. I am new to skis but not to small engines. Where is the air screw on these mikuni carbs? So should I run 8BRES?

  5. #5
    ujustlost's Avatar
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    yes run the 8's, I believe the way it works for NGK the lower the number the hotter the plug, so use BR or BPR8ES's. There are High's and low's on the carbs, download the service manual for the factory settings. Your screws are sized in? are you talking about the ones on the outside of the carb or inside of the carb?

    If your talking about the ones on the outside, take the carb rack completely off and use an inpact screwdriver, you hit the end with a hammer and it puts a quarter twist on it as well as the downforce. As far as the ones on the inside go, are they rusted or just really tough to get out? If there rusted you got water in your fuel system some how and chances are when you go to remove them they will just crumble in a bunch of pieces. If there not rusted then you stand a good chance of removing them. Hope this helps. Mike
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  6. #6

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    There is no doubt in my mind that water got in the fuel from the previous owner. There seemed to be a water line mark on the black rubber piece in the carb and there was a bunch of sentiment in the them. I have not messed with these carbs for settings yet. What bothered me was that this plug was the only one to look this way, and I just replaced that piston and rings Friday. I have not done the best break in on it but I only rode it an hour Saturday, and 5 minutes last night. So everyone thinks it an adjustment issue??

  7. #7
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    If you have a wter line on the diaphragm, you need to open the carbs up. The screws on the inside are loctited from the factory. Use an impact screwdriver to break them free.

    Did you check the filters on the back side of the carbs?

    Get a good look at the piston crown you just replaced through the plug hole.

    If it's all black, you need more fuel.

    Which piston was replaced?

  8. #8
    Hayabusa's Avatar
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    The picture of your plug looks way lean. In fact, that gray color might actually be aluminum deposits from the top of your piston. Definitely go through the carb/fuel system before you run it any more.

  9. #9

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    the cylinder towards the back, by the PTO. If I get rid of the autocock is way I get screw up something. I got rid of it, and just took the fuel line form the pump into carb line. The little clear hose I just capped off. I am going to pull the carbs and try to get them free, but I kept started to strip the screws. I will have to buy an impact screwdriver.

  10. #10

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    ok I think when I took off the auto cock I didn't plug the impluse line or clear line to the manifold. I think air leaked into and leaned out the cylinder. This is why it ran on Saturday before the auto cock removal, and leaned way out yesterday. Could this be right?

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