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  1. #1

    SL750 Piston Mess!! HELP! PICS.

    Okay,

    Took the heads off last night, and here is what it looked like not good at all. The MAG piston was new, but as you can see it melted the side of it.

    As well as burnt a hole in the # 2 piston. The PTO piston looks really black on top and looked like it was going to go soon as well.

    Here are pics of everything. What is causing this? Could I go to a premix and plug the oil pump off.

    Please assist, trashing the SBT piston, and going to a WSM, but what is the reasoning behind this. Also going to a BPR8ES plug,


    Please Advise,
    John
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Click image for larger version. 

Name:	Heads, in order 1,2,3 from left.jpg 
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Name:	New piston, melted front.jpg 
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    Last edited by armyguy7776; 08-12-2008 at 09:25 AM. Reason: spelling


  2. #2
    ph2ocraft's Avatar
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    She's running lean, note no piston wash.
    Have you gone through the fuel system yet?
    New pump
    New Fuel Lines
    Test and/or Replace Fuel Valve
    Rebuild Carbs
    Check Fuel Pick-Up Tubes (depending on year)

    Have you verified crank index?
    What is your fuel pressure??
    You must have 11/2-2 pounds at idle and upwards of 31/2-4 at WOT, no fuel pressure, you get carnage.

  3. #3
    Quote Originally Posted by ph2ocraft View Post
    She's running lean, note no piston wash.
    Have you gone through the fuel system yet? Yes and no.
    New pump Yes, Triple outlet, maybe 2 hrs on it
    New Fuel Lines Yes, fuel lines from tank were in very good shape. Looked to be replaced not long ago. Pick up in tank was new. with new hoses in tank. New hoses to to all three carbs from pump. New hoses to from water separator.
    Test and/or Replace Fuel Valve No I didn't
    Rebuild Carbs No
    Check Fuel Pick-Up Tubes (depending on year) Yes, 1995

    Have you verified crank index? No, how can I do this?
    What is your fuel pressure?? Not sure, can I install a guage to do this?
    You must have 11/2-2 pounds at idle and upwards of 31/2-4 at WOT, no fuel pressure, you get carnage.
    Please understand these are my first skis and I'm not really intelligent on them yet. I'm a mechanic in the military, but of course it's on a diesel.

    Thanks so far,
    John

  4. #4
    Lake Mead Bum & BTLS Mark starflight's Avatar
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    John, You will have to go into your carbs. You will probably find the strainers clogged. Also check the fuel cock for a restriction/ leak.

  5. #5
    Lake Mead Bum & BTLS Mark starflight's Avatar
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    Also , if ya replaced the return line, did ya find and reinstall the restrictor?

  6. #6
    talk to Prochamp!!!! I just had problems with my SL750.....

  7. #7

    Restrictor is there.

    Quote Originally Posted by starflight View Post
    Also , if ya replaced the return line, did ya find and reinstall the restrictor?
    Yeap, it's there.

  8. #8
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Those are 1mm oversized pistons, right?

    Was the jetting ever changed to compensate for the added size?

  9. #9

    Jetting? Not sure.

    Quote Originally Posted by xlint89 View Post
    Those are 1mm oversized pistons, right?

    Was the jetting ever changed to compensate for the added size?
    X,I bought this things used and have no idea. I know this thing is realling ticking me off. I want to figure them out, so it doesn't happen again. Are bpr7es plugs another reason this is happening? Would pre mix help? Going to pull the carbs off and clean them and check the fuel selector valve/switch. Really don't know where to go after that. Thanks, John

  10. #10
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    I doubt the BPR7ES plugs are the issue, but can also add to it.

    Premix has nothing to do with holing a piston, now if it was scuffed or gouged, maybe...

    You have got to check the carbs for sure. A triple outlet fuel pump should also help prevent some issues, but if the carbs are gunked up, a new pump will be useless.

    Do a leak down test if you can also. Just to make sure you are still air tight.

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