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  1. #1
    retro jet's Avatar
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    Reluctant 1996 SLX 780 project

    I have owned this SLX since 98, but it had become too small for my family and our use. I bought a matching pair of basket case GTX's a few years back, but have been busy with other things. My grand plan would have been to sell this ski after I had a running 3 seater, but last summer this ski lost compression in the mag cylinder. So much for that. I wonder if I will be able to recoup the cost of repair if I try to sell it. It is too clean to part out... I guess i will fix it and keep it around, but it will probably be behind the 3 seaters.

    I'm going to lay this out here to keep things straight.
    History:
    bought w/ 42 hours in 98
    In '99 at about 63 hours, center piston skirt broke: measured clearance out of spec. all 3 cylinders.
    Rebuilt with (3) Wiseco .030" over (I think).
    Dealer talked me into reusing crank after they cleaned the debris out of it.
    In '00 Crank let go at 93 hours. Had it rebuilt.

    Current: 230ish hours
    52 PSI mag, mid 120's PSI cen and PTO.
    Inspection with borescope shows mag piston eroded / signs of deto on exhaust side.

    Issues and symptoms:
    Last summer, check valve in primer pump went. Ski started and accelerated fine but would gradually fall flat after coming up on plane. This was run time dependent as if fuel in primer line was being used up. Replaced primer pump and that problem appeared to be solved. Primer draws fuel from supply line, it sounds like the return line is better.
    I cleaned the carbs 3-4 years ago, they were spotless then. I replaced the lines during the first rebuild, which was when the primer was installed.
    From reading the piston wash thread, all 3 piston domes were clean, IE very rich.
    The last few years, I thought at certain RPM and load I could hear a metallic rattle, but it would come and go and was tough to reproduce.
    The engine would run rough and I would simply re-seat the plug caps to smooth out.

    I pulled the pump to take a look at it's condition... The bearings are nice and smooth. Everything works on this ski, even has a perfect mfd. The OP ride plate is a bit crusty.

    So, while this is together and still running, I was going to check timing. I glanced thru the service manual... Is this wasted spark? seemed like 1 trigger.
    Check crank index.
    Check for air leaks.

    I'm open to any ideas or suggestions.

    Click image for larger version. 

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  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    All blue Fuji engines are wasted spark.

    Primer feed from fuel return line is better. Loop the return line low in the hull, tee the primer of the bottom of the loop.

    Fuel pump might want rebuilding. It is critical to always have full fuel pressure with these engines. Weak fuel pressure causes trouble.

    The o-ring seals in the fuel selector valve might be leaking air into the fuel system. Can be rebuilt or replaced.

    Check the seal on the water-fuel separator. Everything should be 100% air tight sealing.

    Piston domes will appear very clean if there is water jacket leaks into the cylinders. Steam cleans the pistons.

  3. #3
    retro jet's Avatar
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    RE: wasted spark So, if I set up a different color mark for each cylinder at whatever base timing is BTDC.* I should be able to see each mark hit with the timing light? Sorry, probably a lot easier if I hit the manual, I have a few minutes to day dream over lunch.

    With reduced fuel pressure or aeration, does any particular cylinder tend to go on these? If I remember right, each carb has it's own supply from the pump. The pistons are evenly light brown with no carbon build up in the center even the one that is eroded. I'll wait until I open them up to make the call, the resolution of the borescope isn't the best. Does fogging oil break down the carbon on the piston?

    Thx.

  4. #4
    BlueFishCrisis's Avatar
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    Do they look like this?


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  5. #5
    BlueFishCrisis's Avatar
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    Quote Originally Posted by retro jet View Post
    With reduced fuel pressure or aeration, does any particular cylinder tend to go on these? If I remember right, each carb has it's own supply from the pump.

    Thx.
    Each piston does have its own supply from the three outlet fuel pump. However, a lean condition which leads to detonation can occur if you have worn components in your carbs ie diaphragms, o rings, needles / seat worn, pop off pressure not set correctly, needle setting not correct, etc. External of the carbs, you may have a leak at one of the crank seals which tend to directly affect the adjacent cylinder, PTO or MAG. A leaky base gasket at one of the cylinders can let air in as can leaky gaskets at the reeds, spacers, manifold, and carb to manifold connections, and crank index out of phase to name a few......

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