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  1. #1
    Sooo...how much for the 780? stimpsonjcat's Avatar
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    Finally, older SLT780 is in the garage...already issues...

    This is my first ski I bought...here is the list from 2012 of what I was planning to do to it.

    -tear down MAG cylinder and replace piston/jug/head as necessary (this piston has some erosion and is down about 10-15psi on compression)
    -fix front exhaust bracket (all bolts are wallowed out)
    -add AAT to pump
    -add trim nozzle to pump
    -add manual trim lever (off a goldwing) to left handlebar
    -trim a set of sponsons back one rib section
    -install Virage batwing rideplate
    -install 115 jets to get richer (and maybe switch to regular gas)


    The NEW plan is now...
    -tear down MAG cylinder and replace piston/jug/head as necessary (this piston has some erosion and is down about 10-15psi on compression)
    -fix front exhaust bracket (all bolts are wallowed out) Will require replacing exhaust pipe as the front fitting is destroyed
    -add AAT to pump
    -install Virage batwing rideplate IF this can be done on the trailer, haven't eyeballed this yet.
    -install 115 jets to get richer (and maybe switch to regular gas)


    This ski suffered an overheat when a friend rode it back to the dock after I had towed it to an island...yep...forgot to remove the clamping pliers. She still runs great, but the front cylinder where the erosion is is now down to 100psi compression.

    I was never able to get the wash pattern where I wanted it on this ski, so the larger jets are going in.

    In other news I had to sell the 780SLX and the shoreport for it to a neighbor as the Corp will not allow 3 ski docks an a dock on Lake Lanier.

    She passed her leak down test last night, so I will remove the exhaust manifold so I can get the busted exhaust pipe out and then time to remove the MAG cylinder and see what we have in there.

    I love my stubby 12mm wrench.

    Lots more room in the SLT than there was in the SLX!


  2. #2
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    I saw a 4 place trailer with 4 slt 780s on it listed on ebay not too long ago. I thought of you right away. You should change your screen name to Mr. 780.

  3. #3
    RLACEMAN's Avatar
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    -install 115 jets to get richer (and maybe switch to regular gas)

    DO NOT use 87 octane unless it has no ethanol, the compression of this engine will not allow it, 89 with ethanol is fine, but you should upjet one size from stock even with that fuel.

  4. #4
    Sooo...how much for the 780? stimpsonjcat's Avatar
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    Quote Originally Posted by RLACEMAN View Post
    -install 115 jets to get richer (and maybe switch to regular gas)

    DO NOT use 87 octane unless it has no ethanol, the compression of this engine will not allow it, 89 with ethanol is fine, but you should upjet one size from stock even with that fuel.
    I do only run ethanol free, but I like the bigger jets anyway.

    I hadn't been here long enough the first time I went through this ski to find out about the jets, but now that she's in the shop, she'll get bigger ones.

  5. #5
    Sooo...how much for the 780? stimpsonjcat's Avatar
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    Quote Originally Posted by Mr. Matrix View Post
    I saw a 4 place trailer with 4 slt 780s on it listed on ebay not too long ago. I thought of you right away. You should change your screen name to Mr. 780.
    I showed that to the wife when I saw it!!! She was...not impressed.

    When I am done with this one I may go back and clean up the 3rd running ski and sell it to a neighbor also.

  6. #6
    Sooo...how much for the 780? stimpsonjcat's Avatar
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    OK, got the exhaust manifold off...what a pain! And then the busted exhaust pipe out. I'll try to take a pic of the failure, I imagine it is fairly common.
    Never thought I would need the spare exhaust pipe. I could probably mill off the uneven part and make it workable, but it would be too thin to survive. I may pick up a new spare pipe, they seem cheap.

    Took the mag cylinder dome off and finally got a good look at the piston. Wow! what a crater! Like I said end of last year she got a bit hot due to me being an idiot, and it almost looks like there is some water cleaning of the piston going on. I'll get a pic tomorrow night and we can discuss it here.

    Tomorrow the MAG jug comes off and the piston comes out and we'll have show and tell. Hopefully it is not too scuffed up to reuse. If it is, I have a box full of jugs to choose from.

    The box I thought had the right jets for this update had only 1 main and one low and neither was the right size...derp. Order outbound to Watcon 10 minutes ago.

  7. #7
    Sooo...how much for the 780? stimpsonjcat's Avatar
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    Here's a pic of the piston...check the crater out!

    Click image for larger version. 

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    Close up of the eroded exhaust-side edge.
    Click image for larger version. 

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    I dragged a small screwdrive blade across the gunk to see how tough it was. It's almost more like a rubber coating than carbon...any ideas?
    Click image for larger version. 

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    Again, this ski has been running great, then end of last season we had an overheat of about 5 minutes. Puter did its thing and went into limp mode, and I got the clamp off the hose and cooled it down with a short run.

    But I am thinking the clean spots on the piston are PROBABLY water incursion...as I was NEVER able to get good wash on this cylinder and it was always running hotter than I wanted.

    Interestingly, the cylinder mikes at 2.808, a mere thou off the spec. I'll check it again several ways from Sunday, but I think a simple hone job and a new stock piston will have this one wrapped up.

  8. #8
    Sooo...how much for the 780? stimpsonjcat's Avatar
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    New jets arrived from Watcon and pop-off adjusted to 21 for all 3 carbs. The MAG was way down at 15! That *IS* the cylinder I was never able to get right...but I don't think pop-off alone could have caused that.

    Also got the jug honed and it looks like it is between 3 and 5 thou over spec...so the inbound +0 piston should be fine.

  9. #9
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    Quote Originally Posted by stimpsonjcat View Post
    New jets arrived from Watcon and pop-off adjusted to 21 for all 3 carbs. The MAG was way down at 15! That *IS* the cylinder I was never able to get right...but I don't think pop-off alone could have caused that.

    Also got the jug honed and it looks like it is between 3 and 5 thou over spec...so the inbound +0 piston should be fine.

    Check your piston to cylinder clearance on that. You may be over spec or at least getting really close if the bore is .003 to .005 too big.

  10. #10
    Sooo...how much for the 780? stimpsonjcat's Avatar
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    Quote Originally Posted by Mr. Matrix View Post
    Quote Originally Posted by stimpsonjcat View Post
    New jets arrived from Watcon and pop-off adjusted to 21 for all 3 carbs. The MAG was way down at 15! That *IS* the cylinder I was never able to get right...but I don't think pop-off alone could have caused that.

    Also got the jug honed and it looks like it is between 3 and 5 thou over spec...so the inbound +0 piston should be fine.

    Check your piston to cylinder clearance on that. You may be over spec or at least getting really close if the bore is .003 to .005 too big.
    I really...REALLY...typed that in all wrong!

    I mean to say the clearance appears to be 0.003 to 0.005...not that much OVER spec.

    But again...I will check the cylinder vs the actual piston when it gets here.

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