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Thread: Please help

  1. #1

    Please help

    I have a 780 Polaris SLT. It idles & runs fine on the trailer but in the water it will not run over 5 mph. All three cylinders have 130 lbs compression. All the carbs have new kits All plugs fire. Reeds are not cracked and fuel valve is bypassed. Still no rpm. Any suggestions are welcome


  2. #2

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    what kinda pumps are you running ?

  3. #3
    My pump is a 3 port oem Brand new

  4. #4

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    check the plug gap should be around .028 and make sure the mixture screws on the carbs are set ?????

  5. #5
    AWA Member 32DegH2O's Avatar
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    In the water, are you able to rev the engine rpms up and the ski just wont go more than 5mph? If so, then you have some stripped splines somewhere. Check the splines of the drive shaft (both ends), impeller and the engine coupler.

  6. #6
    Lake Mead Bum & BTLS Mark starflight's Avatar
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    Have you tried using the choke while running on the water? If so, did it help.If you didn't try it, I would. What are the idle rpms while in the water? Should be around 1200-1300. What were your rpms when doing about 5 mph? Were the internal strainers cleaned (inside the carbs).
    I would suggest pulling the spark plug boots off the wires and clip about a 1/4-1/2" off the wires and twist the boots back on and see how it goes.
    Don't try to keep running it as is. I'd also suggest buying a flexable flash light like the one pictured below to check the wash pattern on the pistons through the spark plug hole in the dome. If the pistons are all black, it's running lean (lack of fuel). Do a search on "piston wash" and you should find pics of what the wash should look like.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  7. #7
    Race, wreck, repeat delagem's Avatar
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    Did the ski run normally, and this is a new condition? Did this just start happening? Or did you just get the ski and this is how it runs?

    5mph suggests you've only got one cylinder actually working. And they will run just fine on the trailer on one cyl, rev right up. But put it in the water....

    How's your compression?

    (My first thought is carbs, but lets eliminate the biggie first! Sounds very similar to the problem I had with my SL650 a few years ago, I just had my hi and lo carb settings wrong on a cylinder)

    Michael

  8. #8
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    The engine will run on the trailer because there is no load on it. Once in the water, it needs to turn the impeller against the resistence of the water.

    I'm assuming that it's only doing 5 MPH because it won't rev up. Is this correct?

    New carb kits:

    Who did the install and are the screws adjusted to specs?

    Was the pop off pressure tested, and at what PSI is it at?

    Were the needles and seats replaced? If so, what size did you install?

    Were the fuel lines installed properly? Return hoses are at the top, while the fuel pump goes to the lower nipples on the carbs.

    Does applying the choke help, hinder, or have no effect on this condition?

    Was the fuel pump installed correctly? And can you test the fuel pressure between the pump and carbs?

    Ignition:

    What spark plugs are installed, and what gap are they set at?

    Try removing the plug boots and cutting the wire back about 1/4" like Star mentioned. Then rescrew the boots back on and re-zip tie them.


    Jet pump:

    If it's revving and not getting up to speed, check for debris inside the water intake.

    Check the splines of the drive shaft, engine coupler, and impeller.

    Check the clearance between the impeller and wear ring with a feeler gauge.

    Did you remove the ride plate and not resilicone it back on? (possible cavatation)


    Please give as much info as possible to better help you. Vague desscriptions won't help much.

  9. #9

    Thanks guys

    I have been out for awhile but I will answer all your questions as best I can. The engine does not rev up in the water but idles fine. I bought the ski like this because the guy could not figure it out. I got it very cheap so I can invest some in it. The fuel pump is new and all the lines are correct. all the carb filters are clean and pressures are good. When I remove the pto plug it is wet with fuel but the plugs all fire fine and are brand new. I will try cutting back the plug wires. The carbs are set at 1 turn out on lows & 1 turn out on highs. I will also try pulling the choke

  10. #10
    Lake Mead Bum & BTLS Mark starflight's Avatar
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    Wet plug? Just 1 is wet? I have on more than one occasion found fuel dribbling out of the main jet while idling. Found the popoff valve not seating, and would flood a cylinder. Could actually see fuel puddling on top of the throttle plate at idle.
    What yr is your ride? Have you down loaded the manual? I looked in the manual, but didn't see carb settings as you have them. 96 had 2 different jets and settings, and 97 had larger main jets and different settings.

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