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  1. #1

    Problems with SL780

    I took the ski to the lake and it ran great until it got low on gas so we went and got some gas but when we got back to the lake it would not plane out. I took it to the shop and they drained the gas out of both ski's mixed it together, added some oil, put it back in and changed the plugs. We took it back to the lake and it ran fine until it got low on gas again, my brother unknowingly took it back to the same store and got gas when he got back it ran like crap. I brought them home to check it out while doing so I decided to remove the plug wiires one at a time and noticed the middle cylinder was not firing right so I decided to check the compression the front and back had 130psi and the middle had 50psi. I went ahead and drained the bad gas, changed the plugs and took it back to try it out, it ran as well as it did before the day before. Today while I was working on the other one I decided to run it for a minute and see how it ran, it sounds as if it would be bogged down if I took it out today. Is there anyway the cylinder could have good compression at some time and not at othersbecause when it is running right it will out run my ski boat, could it do that on two cylinders with a 6'4 270# man riding it. Thanks for the help.


  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Get the engine up to normal temp, and recheck the compression. There shouldn't be intermittent compression. I doubt it would run well on 2 cylinders.

  3. #3
    I just rechecked the compression and they were 130. 60, 130. I put some oil in the cylinderand the compression went up to 125. I guess I will replace that cylinder.

  4. #4
    ph2ocraft's Avatar
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    Can you get us a photo of the piston top, I think it's important you know what killed that cylinder before making the repair.
    Was it detonating?
    Lean?
    Rust on the cylinder (internal surface)?
    How long has it been sitting? Was it fogged? How did it run when it was put away last season?

  5. #5
    I will tear it down today and get some picture. It was ran last season but I am not sure if they fogged it I just bought the pair last week. Thanks

  6. #6
    Here are the pictures it looks like the pistion melted. Thanks for the help.
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  7. #7
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    That's pretty ugly. I would say it looks to have been running real lean.

  8. #8
    How can I check the mixture and correct it? Thanks

  9. #9
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Plug chops and piston wash. The tech section has very good reading about this, do a search for them. But, the jist of it is reading your sparkplugs by running WOT and pulling the lanyard out killing the engine. This should give you a real good idea how the engine is running internally. Now piston wash is a little tougher, but gives accurate description of what's happening inside. You need a special light to see the tops of the pistons to look down the plug hole, OR you remove your heads. What you're looking for is a black center with just a hint of clean piston tops around the outside. All black tops is lean, (like in your pic) and clean tops is too rich. You want about a 85-90% black piston top with the rest being clean or light brown. There are some pics of piston wash in here if you do a search.

  10. #10
    ph2ocraft's Avatar
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    tucker, the photo's are what you replaced a short while ago or what you just had in the engine?
    You have a severe detonation issue happening there.
    Can you give us a little more history on the engine?

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