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  1. #1

    Another SL750 problem

    Hi to all and thank you for having a great site. First time posting but i have used this site a great deal. I picked up a 94 sl750 that had a burnt piston. With the help of this site i have completly rebuilt the engine and fuel system. First couple of rides were great and the ski was running top notch... until i burnt another hole in the pto piston. i will list all things i have done in the hopes someone can give me some thought into why it may have happend again. i have purchased another piston and im ready to install but leery to proced until i find a root cause. any thoughts?

    -all 3 jugs machined .50 over
    -new pistons and rings
    -new carb kits and reed valves
    -new crank bearings and crank in proper phase
    -new triple fuel pump
    -new fuel lines
    -new gaskets
    -new spark plugs
    -all carbs set to the shop manual specs
    -oil block off plate and still running at 32:1 for breakin

    the only part of the fuel system left factory was the primer bulb which may have a few cracks but not leaking

    help!


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Primer bulb

    Fuel system needs to be AIR tight forward of the fuel pump. Air leaks can cause lean conditions.

    Exactly what carb settings were you using?

    Are these the original carburetors for this engine?

    Do you know what jets are in the carbs?

    Was the fuel tank also cleaned out?

    Fuel selector valve replaced or rebuilt?

    Were you monitoring piston wash patterns during your break-in process?

  3. #3
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Silly question, but did you use new crank seals?

    Did you do a leak down test?

    Good gasket seal between carb and intake manifold?

    No fuel pump problems? (put 5" of vacuum on the fuel pump diaphragm. It should hold indefinitely)

    Loose pulse hose connection?

    Crack in pulse hose?

    Pulse hose fitting work loose?

  4. #4
    BlueFishCrisis's Avatar
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    Pulse line under 12"?

  5. #5
    wow, thanks for all the quick replys
    yes i used new cranks seals, the fuel tank was cleaned out(lots of debre in before), fuel selector valve was replaced, not sure what size the jets are and carbs are still factory carbs.
    the fuel settings i used are
    low speed 1/2 turn
    mag 1 1/4 turn
    cen 3/8 turn
    pto 7/8 turn

    pulse hose is new and about 11 inches long

    i checked piston wash after about 2 hours of riding and it looked not bad but hard to tell cause the motor was still pretty fresh and i never got to check again before burnt the piston

    how often should i check piston wash while in breakin period?
    do the carb settings look ok for a new tripple fuel pump?

    any thoughts

    thanks

  6. #6
    BlueFishCrisis's Avatar
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    Quote Originally Posted by xlint89 View Post
    Did you do a leak down test?
    Was a leak down performed?

  7. #7
    BlueFishCrisis's Avatar
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    I regularly do plug chops while I am riding, especially after tuning adjustments, to monitor the fuel mix. It is tough to constantly check the wash while on the water...

  8. #8
    I did not do a leak down. i will be installing the new piston tonight and will do a leak down test
    do my carb settings look ok. should i try and richen the pto a bit before i even start up?

  9. #9
    BlueFishCrisis's Avatar
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    Settings are ok for factory, never hurts to fatten them up a bit.....

  10. #10
    BlueFishCrisis's Avatar
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    What spark plugs are you running??

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