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  1. #1

    '96 780 SL vs. '94 750 SL SLT Fuel usage

    I was out with my 780 SL and my bro-in-law has both 750 SL and SLT. I seem to be using more fuel. My 780SL vs his 750SL we were going the same speed and doing the same things but I ran out of gas and had to be towed back by his SL. This seems to be the same theme everytime we go out.

    After I re-fueled, he kept going and never hit reserve. I have looked for fuel leaks, pressurized my tank w/ 5psi and changed all the fuel lines. I even put UV dye in the gas and I don't see a leak anywhere but I do smell gas odor when I remove the seat. I am getting about 45mph top speed and the engine runs very smooth. Is it just the 35cc difference or do the carbs need to be rebuilt or adjusted??? Even his SLT didn't need fuel and he was riding 3 people at one time. Guessing, I would say I used 3 to 5 gallon more.


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Was your gas tank actually empty when the engine stopped running?

    The rated tank capacity is 9.8 gallons. When it is empty, how many gallons does it take to fill it?

    Any aftermarket parts or modifications on either your 1996 SL 780 or the 1994 SL and SLT 750?

    Are the carbs original/stock on your SL 780?
    Is isn't an SLX 780, is it?

    Have you checked cylinder compression?
    Weak compression will reduce fuel economy.

    What RPM are you seeing at WOT?

    What is the condition of the jet pump impeller and stator?
    Blade clearance?
    Blade or vane damage?

  3. #3
    This is a '96 780 SL not SLX.

    All stock. I have the black carbs and the 750s have the blue. I haven't checked the compression recently but it was 125psi on all cylinders 3 weeks ago and I was experiencing the same thing.

    I filled the tank and I looked at it with the toolbox out and it was at the top of the tank. It actually quit.

    I get about 6200 rpm WOT. The pump blades look smooth and clean. How do you measure clearance? I don't know about the stator. I get like 15V when running WOT. How can you check the stator?

    The spark plugs are a nice chocolate brown too.

  4. #4
    SPEED KILLS, BUT YOU GET THERE QUICKER Keddano's Avatar
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    He's referring to the pump stator,I has the 5 vains that directs the water into a smooth flow. Yes, there are 2 different types of stators on a ski.


    Ask pirate.....Post #265

    http://www.greenhulk.net/forums/show...stator&page=27

  5. #5
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by WaveChaser View Post
    ... I filled the tank and I looked at it with the toolbox out and it was at the top of the tank. It actually quit.
    How much fuel did you add to go from 'out of gas' to 'tank is full'?

    I get about 6200 rpm WOT.

    The pump blades look smooth and clean. How do you measure clearance? I don't know about the stator...
    Impeller blade clearance is checked using calibrated feeler gauges.

    The thickest gauge feeler blade that will just slide between the impeller blade outside edges and the surrounding wear ring surface tells you the blade clearance.

    You can measure this with the jet pump mounted in the ski, no dis-assembly required. Thin hands and long feeler blades may be needed, and it might be easier to measure the clearance by reaching through the intake grate.

    Maximum impeller blade clearance is 0.020", and a good condition jet pump will have less than 0.010" blade clearance.

    The jet pump stator is the section with the fixed blades, that doesn't spin, located right behind the impeller. If the stator blade edges are bent or beat up, it can reduce jet pump efficiency.

    If the impeller blades are badly dinged or bent, that can also reduce efficiency.

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  6. #6
    Bing-A-Ding-Ding-Ding, Brrrrrap! Brrrrrrrrrap!!! Polaris_Nut#1's Avatar
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    how bout the obvious the SLT has an 11 gallon tank

    opps read it again, sl and slt 750 hmmm?

  7. #7
    rob2337's Avatar
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    I also find that when tanking the SL model, you need to have it tilted a bit to the back of the hull on the trailer or in the water. I can fit about 2 gallons more when I tilt my SL back and "burp" it when filling. If you have a trailer that tilts forward, (ie a low hitch on your car) you won't be able to fit that much gas in before it comes to the top of the filler.

  8. #8
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    The 780 makes 12 more HP than the 750 and has slightly larger jets. Should burn more fuel.

    HOWEVER, you say you're doing the same speeds as he. Which shouldn't be using tons of fuel.

    Your MPH seems low for that ski turning 6200 RPM. Should be more like 48,49, 50 MPH.

    Was your BIL set up with another impeller by chance? Maybe he's turning lower RPM than you at the same speeds.

    How hard are you nailing it out of the hole? That will burn more fuel than a gradual increase.

  9. #9
    Bing-A-Ding-Ding-Ding, Brrrrrap! Brrrrrrrrrap!!! Polaris_Nut#1's Avatar
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    SL750
    744cc
    10.5:1
    24* at 3000 rpm
    80 hp at 6000 rpm
    4 blade 5131079

    SL780
    779cc
    11.85:1
    90+hp at 6250rpm
    4 blade 5131079
    50 mile WOT

    the specs are very close

  10. #10
    Bing-A-Ding-Ding-Ding, Brrrrrap! Brrrrrrrrrap!!! Polaris_Nut#1's Avatar
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    Quote Originally Posted by K447 View Post
    Have you checked cylinder compression?
    Weak compression will reduce fuel economy.

    What RPM are you seeing at WOT?
    2 votes for a compression check
    he should be going faster than 45mph

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