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  1. #1
    seaobin's Avatar
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    750 SL ate itself today

    Happy Spring to all. 82* and beautiful in Raleigh, 53* water temp so what the hell lets go skiing. Last week I drained the fuel, refilled with fresh, added new cooling through hulls, recovered the seat and went through the fuel lines and carbs. Everything looks great

    Went out and the ski was running well. 6010 and 50.1 on DOM (48.3 on GPS) so I pulled the plugs. (Brand New)

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    M-C-P in order PTO looks alittle leans so 1/4 turn out to richen it up.

    THe ski started to act a little halfway back tot eh dock and I babied it back. Temps on all cylinders are good to cool, good flow through the engine. I get back to the dock and cannot keep it idleing through the no wake zone. I pull it out and pull the heads and find myself a spring present. M-C-P
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  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Hard to tell from the photos - is that mechanical damage/pitting in the center cylinder head?

    What are the black speckles in the MAG head? Also pitting?

  3. #3
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Please remember that cool temps will affect jetting needs.

    6010 RPM is low. Should've been closer to 6300 RPM. (first warning that something is amiss)

    Mag piston has damage from debris. Most likely the cause of the pitted head.
    I'm baffled by the damage. Looks as if something got snagged on the pistons down stroke.

    Does it have signs of seizure on the cyl walls?

    CEN looks like detonation. Esp damaged around exh port.

    Both were very lean.

    Plug readings mean nothing if you idled back to the dock. Need to "read" them directly after a WOT run.


    Was any damage done to the heads from the previous piston replacements?

    Were any mods done to the heads after the oversized pistons were installed? (.5mm isn't too bad, but .75mm is really in need of enlarging the heads to match the pistons)

    I'd suggest conducting a crank index test and see how "gritty" the bearings feel.

    Are you looking to rebuild this? I've got good deals on a 750 and 780 top end package deal if so.

  4. #4
    seaobin's Avatar
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    Yes I am going to rebuild. Was planing on going to 1 over and replacing the heads. There was a little damage from previous meltdown.

    I have never seen 6300 on my 750 and had great wash last fall. It has always been around 6100. Figured I was rich, not lean, especially the way the plugs looked

    AS for seizure marks, mag yes, center no

    Mag looks like 4 corner seize

    Another $500 mistake



    center crown looks like a bb shot around inside

    ---------- Post added at 08:29 PM ---------- Previous post was at 08:27 PM ----------

    Bearings all feel good. I am going to tear down tomorrow and see what I have

    ---------- Post added at 08:41 PM ---------- Previous post was at 08:29 PM ----------

    So I need a top end kit and someone to update teh heads for 1.0 over

  5. #5
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Black sooty plugs on a 2 stroke are lean.

    Nice brown/chocolate color is perfrect

    White and dry is extremely lean.

    White or clean and wet is rich



    Cool water temps, lean conditions = piston expansion before the cyls expand.



    I have a brand new 750 WSM .5mm top end kit, plus 3 cyls and heads already bored for $250 plus shipping.....

  6. #6
    seaobin's Avatar
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    pm sent

    does it come with gaskets or do I need to order those as well

    ---------- Post added at 09:20 PM ---------- Previous post was at 09:06 PM ----------

    yes it is pitted very badly.

    I think Mag lost a ring

    Center deto'd

  7. #7
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by xlint89 View Post
    ...Cool water temps, lean conditions = piston expansion before the cyls expand...
    Quote Originally Posted by seaobin View Post
    ... Mag looks like 4 corner seize ...
    Was the thermostat and/or pressure by-pass valve removed from this engine?

    No thermostat to control engine temp means more risk of cold cylinder seize when riding in cold water.

  8. #8
    seaobin's Avatar
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    Yes I have straight triple outputs, no water bar.

  9. #9
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Quote Originally Posted by seaobin View Post
    pm sent

    does it come with gaskets or do I need to order those as well

    ---------- Post added at 09:20 PM ---------- Previous post was at 09:06 PM ----------

    yes it is pitted very badly.

    I think Mag lost a ring

    Center deto'd
    Comes with gaskets. New WSM top end kit sealed in package.

  10. #10
    seaobin's Avatar
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    I got a present today.Click image for larger version. 

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