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  1. #1
    work hard..play harder! gruba's Avatar
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    Question sl780 compression

    I recently picked up a 96 sl780..it starts easily nad seems to run fine...although I have not had it in the water to really test it. What should the comp. be? I checked it, all 3 are the same at 102-103. I don't have a manual yet, so I need some help. Thanks


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by gruba View Post
    I recently picked up a 96 sl780..it starts easily nad seems to run fine...although I have not had it in the water to really test it. What should the comp. be? I checked it, all 3 are the same at 102-103. I don't have a manual yet, so I need some help. Thanks
    Welcome to the Hulk!

    You can find the 1992-1998 Polaris Service Manual here.

    The compression numbers you posted are low, but the same reading across all three cylinders. Usually, this implies the gauge you are using is inaccurate, or you were not holding the throttle wide open while testing the compression.

    Normally, compression numbers would be 120PSI or higher, with all three cylinders within 10% of each other, or closer.

    PWC engines can seem fine out of the water, but still have problems when actually running in the water. If you can water test it, that is the best way.

    It should start fairly easily in the water, and idle smoothly once it starts to warm up (1250 RPM). Once warm, max engine RPM on smooth water (as shown on the MFD display) should be steady, and around 6,500RPM, give or take a little.

    The MFD speedometer is not 100% accurate, so focus on engine RPM to gauge engine health.

    There should be no significant water leaking into the hull while you ride.

    Has the machine been in regular use recently? The main area of concern is the fuel system and carburetors. Carbs that have been sitting, or have not been maintained, often need to be taken apart, cleaned, and rebuilt, to ensure long engine life. An internally clogged up carb can ruin an engine in short order, even if the engine seems to be running OK.

    Fuel lines and filters - If these are original (and therefore over ten years old), they should be replaced with new fuel hoses. Some models even have fuel hose inside the fuel tank, which also should be replaced.

    Once this sort of basic maintenance has been done, these blue Fuji engines are quite reliable. The 780 is the largest Fuji engine Polaris used, other than the racing oriented Pro 785 model.

    1997 was the last year for the Fuji engines in Polaris (other than the Pro 785). Polaris began using their own 'domestic' engines starting in 1996, and phased out the Fuji.

  3. #3
    work hard..play harder! gruba's Avatar
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    sl780

    thanks , was not holding throttle open, will check compression. The prior owner says it had been run up to this fall..then winterized. Hoses all look good, small amount of water in engine compartment, enough to soak up with towels. I don't have the ability to water test right now. Thanks for the info. I'm sure I'll be back!

  4. #4
    Lake Mead Bum & BTLS Mark starflight's Avatar
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    Quote Originally Posted by gruba View Post
    Hoses all look good
    Outside appearance will not tell the whole story. If they are the grey Tempo brand fuel lines, they break down internally, and will send a green goo to your carbs and clog the internal strainers in the carbs.
    If they are the Tempo lines, change them and check/clean the carbs.

  5. #5
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Welcome to the Hulk.

    Compression should be done on a warm engine. Readings may be a bit lower on a cold engine as nothing has expanded yet.

    As long as all 3 are consistant, run with it. Unless you want to sink another $400 into it to bump up the compression a little.

  6. #6
    work hard..play harder! gruba's Avatar
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    compression is fine, i borrowed a friends gauge, mine apparently no longer works...120 ,119, 117, in that order.

    on another subject...the ski has been beached a few too many times and the nice factory finish is worn off the very front of the hull. What can i use to fill it in, smooth it out and maybe coat it with? There is no apparent breach in the hull, but the factory finish is worn off in about a 10 x 10 inch area.

    i will check the hoses again, if they are that type i will likely take your advice.

  7. #7
    Welcome to the Hulk!

    I heard what these guys were saying when I first joined, but didn't listen. (see pics)

    I would replace ALL the lines and rebuild the carbs. I'm guessing the 780 must come with a triple outlet fuel pump, or the guys above would have chimed in. That was my first upgrade after replacing the fuel lines/filters and rebuilding the carbs.
    Attached Images Attached Images      

  8. #8
    work hard..play harder! gruba's Avatar
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    I am intending on tearing apart and doing the carbs...i have read about that on this forum before i signed up. thanks for the advice, i will be replacing some fuel lines.

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