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  1. #1

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    Need help adjusting the carburetors

    ok, I just rebuilt my SL 780 and are currently trying to adjust the carburator. I got it started. but it is kind of werid, I am performing the idle speed adjustment.
    I copy the following from the manual and marked them with numbers to ask my questions. By the way I have the drive shaft remove so that it will not cause any damange.
    the book said,

    1) turn the low speed screw until it is lighly seated, then back out about 3/4 to 1 turn.
    DONE.

    2) then run the engine until it reached the operating temp.
    DONE the engine is running at 3000rpm

    3) then With the engine operating, slowly rotate the throttle stop screw until the engine idles at 1,200 to 1,300 rpm.
    Done have some problem here as the speed went up and down too fast and finally stop at 1220 - 1300 rpm

    4) Next, rotate the low speed screw inward or outward 1!8th of a turn at a time until the cylinders fire evenly and engine rpm increases.
    How how do i know if the cylinders fire evenly????and adjusting the needle did not increase the RPM...

    also at that adjustment the engine cannot start back up , i have to give it a little gas before it could start again then go back to 1300rpm.
    at this point I have a feeling the gas is not running evenly. I did a simple test by pulling the start plug one at a time to see what happed.
    when I put the MAG, the engine keep running whit a little reduce in RPM then it finally die. then I put it back and pull the center plug and the engine keep running with no sign of the RPM reducing. Then i put it back and pull the AFT. the engine die almost immidialy.

    I did the commpression test when the engine is warm and it read 125, 125, 120 from mag to aft.


    OK here is some update:
    I noticed the idle rpm is going up and down. some time it is 1200 - 1280 the with out touching anything it will goes to the range of 1300 - 1400, then it will goes back down...... when i shut off the engine, it will not restart unless i give it a little gas. the hold on to it for a few seconds and then it will stay running.
    Also one more then I notice that the center carburetor adn the front carburetor start to have fuel "building up" as indicated in the picture attach. more on the center carburetor less on the front and none on the rear one. What is wrong?


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  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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  3. #3

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    thanks for the info. I read most of them..... but the more I read the more confuse I get.
    some instruction said that to turn the need 1 1/4 out some said 3/4 out? which is right?

  4. #4

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    if that one carb is the only carb loading up with fuel my guess would be to turn out the low speed screw some.

  5. #5

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    Quote Originally Posted by hartman View Post
    if that one carb is the only carb loading up with fuel my guess would be to turn out the low speed screw some.
    ok turn it out more? wouldn't that give it even more fuel?

  6. #6

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    the load up of fuel seem to be a one time thing, I ran the ski on garden hose for a few more time and didn't see the builtup any more. One new thing i discover thought, I think the center cylinder might not be running on idle.
    when I took out the plug for MAG during idle, then engine lost a little rpm but still running. when i unplug the center, the engine RPM stay the same. When I unplug the end cylinder, it die. ofcause this was done one plug at a time.
    Then i continue with 2nd test I saw on video on this forums. is the Run the engine with only one cylider at a time but give it a little more gas, they all run fine but will die when i release the gas.
    One more reason that I don't think the center cylinder is running during Idle is that, both the front and back cylinders is warm after running it for a little bit, but the center one remain cool.

  7. #7
    All low speed adjusters should be set at 7/8 turn out. High speeds are PTO= 1 turn CEN= 3/4 turn MAG= 3/4 turn.

    Also, the idle RPM is supposed to be the idle RPM in the water... I dont know the exact number for RPM out of the water but I think it is around 3000. This is because of the load put on the engine from the jet pump in the water.

    When you say you rebuilt it does that mean you rebuilt/cleaned the carbs too? It sounds like you may have a blocked low speed jet/bypass which is making the carb pull fuel through the high speed at idle causing the fuel buildup.

  8. #8
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    What year is your ski?

    Sounds like it may be a bad check valve inside te carb. (clear plastic "flap" on the jet block)

  9. #9

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    Quote Originally Posted by a_kraker99 View Post
    All low speed adjusters should be set at 7/8 turn out. High speeds are PTO= 1 turn CEN= 3/4 turn MAG= 3/4 turn.

    Also, the idle RPM is supposed to be the idle RPM in the water... I dont know the exact number for RPM out of the water but I think it is around 3000. This is because of the load put on the engine from the jet pump in the water.

    When you say you rebuilt it does that mean you rebuilt/cleaned the carbs too? It sounds like you may have a blocked low speed jet/bypass which is making the carb pull fuel through the high speed at idle causing the fuel buildup.
    ok, i am running the engine without the drive shaft as xint89 mention that i cannot run the engine too long if the driveshaft is attached. now, I have try the low speed 7/8 turn, but my engine would not stay running unless i adjust the side screw to open the butterfly valve a little, just a litlle. Now image all this is without any load..... i don't think it will make it inwater with everything attached.

    Quote Originally Posted by xlint89 View Post
    What year is your ski?

    Sounds like it may be a bad check valve inside te carb. (clear plastic "flap" on the jet block)

    The ski is 96 sl 780. I rebuilt the engine and the carb. however i only replace the diaphragm as all other parts look clean. is there a way for me to just get the plastic "flap".

  10. #10
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    1996 SL 780

    Main jet 107.5

    slow jet 72.5

    High speed screw M=3/4 C=3/4 P=1

    low speed screws 5/8

    Idle in water 1250-1300 RPM

    Pop off 20-24 psi



    Yes you can get just the clear plastic "flap" (anti siphon valve)

    But I would also suggest getting new needles and seats (2.0 push in type) due to age.

    I know you can get the valves from atlanticjetsports.com for sure. But you can see if John Zigler or Sharp's marine can get them for you too.

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