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  1. #1

    93' SL750 Compression Test...Good or bad???

    I did a compression test on each cylinder head. Im a little confused here are the results.
    #1 Head - 118 PSI
    #2 Head - 118 PSI
    #3 Head - 112 PSI
    Is that significant, and will that cause my ski to go really slow? I have replaced all the pistons, and a new jug on #1, took it out and with full throttle it ran at half speed and very slow response. By the time I got back to the dock, it would keep stalling. Thats when I did the compression test. I just tok off the carbs, ready for a breakdown and reassembly, but if it's the heads again, Im getting rid of this thing.


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Did you test compression when you first got the engine back together, before you ran it?

    Have you confirmed strong spark on all three cylinders?

    Carb screw settings?
    Choke is not stuck closed?

    That all three cylinders are showing very similar numbers implies that all three are in the same condition. If you have access to another compression gauge, that might be helpful. If your gauge is reading low, that would be good to know.

    When you changed the pistons, were the cylinders honed or bored out? What piston size(s) are you using?
    New rings?

    What else did you touch on the motor?
    Flywheel or electrical stator?

    What do the spark plugs look like?
    Any oil or water fouling?

  3. #3
    I ran it first before I did the compression test. Im not sure what size pistons, Whatever the stock pistons for the 750 of that year is. The jugs were an original bore. Replaced the rings, I am getting a nice spark on all three. #1 and #2 plugs were wet, gas maybe, the 3rd was dry. Did not touch the stator or flywheel. It could be the carb. screws, but Im afraid to mess with them, unless someone has a picture and detail of setting them, but I have not touched them. Should I??? I do know that the compression rating for that year and make is 120 PSI, and I bought a chinese made meter, it could be off a little

  4. #4
    Moderator beerdart's Avatar
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    What caused the engine to fail the first time?? Have the carbs ever been cleaned/rebuilt?

  5. #5
    Carbs. were never cleaned. there was a hole in #1 and it warped the jug, so I replaced the pistons, 1 jug and new triple fuel pump

  6. #6
    What should I do about the Screw settings. Im almost sure something is not right. I don't have a clue how to set them though.

  7. #7
    Moderator beerdart's Avatar
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  8. #8
    Moderator beerdart's Avatar
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    You need to go thru the carbs..

  9. #9
    If I set the screws from what the manual tells me, I'll be driving backwards. I just can't understand how they want me to turn them

  10. #10
    Moderator beerdart's Avatar
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    To adjust turn them in all the way until lightly seated and back them out the # of turns stated in the manual. You really need to inspect the insides of the carbs first.

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