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Thread: 780 slx

  1. #1
    tankray78's Avatar
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    780 slx

    After stalking these forums for several months gathering very useful and abundant information, I have recently joined.
    I picked up a 96 780 slx about a year ago and have been going through it before i attempt any water ventures.
    From what I can see (and was told by previous owner) the ski is basically stock, with the exception of: op fa's, op ride plate, and an r&d intake grate.
    I just got done installing a new starter and associated relay, while I'm awaiting the exhaust to come back from the pcoat shop...I figured I would get some
    compression numbers before I reassemble, if for nothing else piece of mind. Here's what I got: PTO 140, CEN 141, MAG 141
    The MFD claims 78 hours. Are these numbers normal? Or do they indicate some internal mods? Thank you in advance guys!


  2. #2
    Those numbers arnt bumped up too high. It might have been recently rebuilt or have just really been babied. My 95 with the original engine that has never been opened up is around 125-130, and that thing has some long hard hours on it, yet I can hold it wide open all day accross the lake and never second guess the machine as it runs pretty well for a ski of its age.Tthats hard to tell without looking at it or opening it up but my guess is probly stock. If anything take confidence in that you have a nice healthy engine. At about 140psi, I would recomend running 91 oct or similar to be safe along with some high quality oil and you should be ready to roll.

    Also, if someone was going for high compression it would probably be closer to 160 ish, otherwise there would be no real gain.

    I hate saying this as someone will probly chime in and give a second opinion, but well you have it apart rip the oil injection off and go to premix at 40:1. It really isnt worth the risk on a 15+ year old ski. People will say the pumps dont wear out, its the lines that go and cause the failure, but for the cost of the hoses and clamps you could just as easily remove the oil pump, pull the shaft, put the pump back in, pull the tank, stick a resistor in the sender line, and never have to worry about it again. This is all assuming that this hasnt already been done.


    Good luck with the ski, sure they arnt the fastest or most stylish ski on the lake, but for very little money and labor you will have a fun, dependable ski that is stable enough to ride 2 on, or throw it into a flat spin and throw your self off of it

  3. #3
    Also, if you havnt already, rip all of the fuel system apart, rebuild the carbs, put a 2 or 3 output pump on it, remove the autocock, and replace the lines, you will be happy you did.


    http://www.greenhulk.net/forums/showthread.php?t=148277

  4. #4
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    The 780s already have a triple outlet fuel pump. no need to change the pump. The oil injection system is fine if it is maintained. New lines and clamps and you should be good to go. If you do choose to go premix, remember you will use about double the amount of oil you are used to using, so thats something to consider as well. Oil injection is really a personal preference, there really is no right or wrong answer. Just be sure you maintain the system.

  5. #5
    tankray78's Avatar
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    Thanks for the advice guys!

  6. #6
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Welcome to the Hulk.

    Actually the only thing aftermarket on the SLX you have is the OP ride plate. The FA's and the R&D intake grate came on it from the factory.

    140 psi isn't really normal. Usually 120-135ish is.

    However, it isn't too much to run pump gas on. I would run premium fuel just to play it safe.

    And yes, you already have the high output fuel pump on that ski, and there is no autocock to remove. Those mods are for the older 650 and 750's.

    It's no a bad idea to replace the fuel and oil hoses though. And a carb rebuild would be a good suggestion due to age alone.

  7. #7
    tankray78's Avatar
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    XLINT thank you for the insight, and the welcoming. I run premium in everything these days from my scooter to the chainsaw!

    Carbs are good I just rebuilt them and they were suprisingly clean, I'm changing out the lines now.

    Just replaced the fuel on/off switch... should have seen the corrosion and hose frozen to it!

  8. #8
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Petcock is a good thing to replace as well. Forgot to mention that one.

    I hope you used genuine Mikuni carb rebuild kits?

  9. #9
    I transcend race Hombre! TBone14's Avatar
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    You can also rebuild your fuel pump for cheap.

  10. #10
    tankray78's Avatar
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    I got the kits from sbt, i belive they are genuine mikuni...never thought about that.

    Havent done the pump yet but will soon.

    Took her over to the lake today, fired right up and runs good....revs up but wont go??? any suggestions?

    Moves around at idle but hit the throttle and it revs up, but isnt hooking up for some reason. impeller looks good/no obstructions????

    HEEEEEEEEEEEEEEEELLLLLLLLLLLLLLPPPPPPPPPPPPPPPPPPP P!!!!!!!!!!!!!!!!!!!!!!!!!

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