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  1. #1

    Join Date
    Aug 2014
    Georgia (lake lanier)

    1999 yamaha GP760 no compression on rear cylinder

    Newbie to wrenching on skis, so bear with me.

    Kids told me ski would not stay running. Also found out the ski had been running slow for the past few weeks so I suspect a lean condition.
    Pulled ski into garage to check compression. 140psi on the front and 20 or less on the back.
    Have not pulled head, but just starting to think of possibilities. If top end job is needed does engine meed to come out of ski, or should I plan on pulling it regardless?
    I am sure more questions will follow as I get into this. Never worked on 2 stroke stuff, but have done plenty of automotive rebuilds.

  2. #2
    This is how I run a jetski shop in the desert nmpeter's Avatar
    Join Date
    May 2008
    Elephant Butte New Mexico
    welcome to GH!

    I would prefer to do the top end work with the engine out of the ski, but many do it in the ski, but it is far trickier. Since you are pretty much down to the shortblock anyway, I'd pull the entire thing. Pull the head and see what the real damage is. Lots of metal bits from a busted up piston flying around may change your gameplan a bit,

    Yamaha motors are not inexpensive.

    In the meantime..start reading....

  3. #3

    Join Date
    Aug 2014
    Georgia (lake lanier)
    Thanks, guess I will work toward pulling engine. Will pull head first and post some pics. See how it goes.

  4. #4
    Myself's Avatar
    Join Date
    May 2007
    North Central Arkansas
    Done pretty easily in hull on that model. Need to pull cylinder first to inspect crank. If there is a lot of particulate then I would suggest pulling so you can tip it over and flush it out (diesel fuel works good). If there is actual metal debris floating around you should do a full teardown and rebuild.

  5. #5

    Join Date
    Aug 2014
    Georgia (lake lanier)
    Sounds like pulling it is the safe thing to do. Probably the best way to learn my way around with these things. From what I read here, they dont seem too bad and once you put one together it sounds like people get addicted. I have seen several nice skis around with blown engines. If they are half as much fun to wrench on as they are to ride it may make a good hobby. Anyone here from Ga? I am on the north endvof lake lanier.

  6. #6
    I picked up a fried out gp760 last winter. It was a piece of cake to rebuild. I didn't split the cases but that would of been easy too. Download a manual for free somewhere and pick up a good torque torque wrench, although my harbor freight one does me fine. I know I know....

    I pulled the engine and kept the exhaust as one piece, to avoid buying gaskets, and used a gas leak down gauge from home depot to pressure test, blocked off intake holes with 1.5 inch Oatly expanding plugs while using the seals out of the 2 inch plug.

    I went to hobby lobby and got 12 rare earth button magnets and put on my crank to help pick up debris while flushing out the bottom end.

    I had Full Bore Online do my cylinders, took about 3 weeks and was 375 for a wsm gasket kit and pro X pistons.

    If you can do work on a car engine, you'll be fine working on a ski engine. I can rebuild 650's and 701's all day with my eyes closed, but am afraid to split the cases on my XR650L to put a kick starter on. Seems really complicated.

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