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  1. #1

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    Unhappy 97 780slt polaris driving me nuts please help sandonut

    new-bee to sight. 97 780slt starts fine, w.o.t. 6800 rpm 4 sec. starts decline in rpms 6800, 6750, 6700, 6650, ect. Declines to about 3500-4000, rev-limiter disconnected. Kill the engine, start it back up, 3500-4000. Wait 3 to 5 min. start it back up 6800, 6750, 6700, 6650, ect. declines to about 3500 to 4000, no power, just bogging down on the hoes in the water riding or on trailer. Have 96 780sl for parts. Tested stater, 97 780slt was 225 oms on trigger coil, 96 780sl was 215 oms, all others were OK. 96 780sl was 215 oms on trigger coil, was 84 oms on the pulsar coil. Changed stater, fly wheel, cdi box, temp censer, mfd, cleaned carbs, changed all fuel lines & vacuum hoes, ( 50 psi. fuel injection hoes ) ran the same, a little smother at idle, ( was trash in stater carb ). Had restrict-or in stater carb return line, drilled it out ( has 0.020 in each carb ), no change, ran the same. Has 3 port fuel pump. Put fuel tester gauge between fuel pump & carb on each port 5 psi after running a few sec? Not sure how to test fuel pressure, are pop off pressure? Changed carbs and one port fuel pump to 96 780sl. Ran better 6840 rpms for 10-15 sec. killed engine, started back up same thing, 6800, 6750, 6700, 6650, ect. thought I was a manic, certificated in transmissions, diesel engines, gasoline engines, fuel injections. Worked on snowmobiles, boats, pwc. 18 wheelers, 4 wheelers, all kinds of combustion engines. Fuji engine kicking my tail. Help!


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Why would you drill out the fuel return restrictor?

    Have you removed and checked the jet pump? Bad jet pump impeller bearings can bind up and put a drag on the engine.

    The RPM winds down despite holding the throttle open, on the trailer, correct?

    That suggests either an ignition problem or a mechanical problem. Fuel delivery seems less likely as an unloaded engine should still be able to rev up despite poor fuel delivery, or even one cylinder not firing at all. Unless the fuel delivery is completely starved or sucking in a lot of air.

  3. #3

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    yes, jet is removed. Yes rpms wind down on trailer, in water, jet installed, jet uninstalled, on hoes same. Drilled restrict-or out because, some models do not have. Bought pwc with problem. Did not know what other persons did, changed carbs?. 96 780sl had no restrict-or?.

  4. #4

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    checked compression all 3 130-135.Not sure about vacuum test.Spray carb-cleaner on carb base, reed valve gasket area,crank case? (please help beside my self) Thanks in advance

  5. #5
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by sandonut View Post
    yes, jet is removed. Yes rpms wind down on trailer, in water, jet installed, jet uninstalled, on hoes same...
    If you run it on the trailer DRY without water cooling, does it rev up and maintain RPM?

    You can do this without water on a cold engine for maybe 20 seconds or so.

    I am wondering if you have a water leak that is getting into the cylinders when the engine gets warm.

    BTW, hoes is not the same as hose

  6. #6

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    yes I know my spelling lacks L.O.L,my spell-checker missed that one & my grandsons too. See grandsons & I are doing this together (12 & 13 years old).We also have & ride,84 Kaw.440 piped,87 Kaw.440 piped,87 Kaw 550 piped,91 Kaw. 550sx piped,89&90 650&500 Yamaha,87 Fun-Jet (boat).Fixing the Polaris to ride & for Fly-Board come spring.(You-Tube Fly-Board you"ll see what I"m talking about).Yes 54 & still NUTS!,that's why thy call me San-Do-Nut,my name is Sando.Just to let you know a little bit about us. Yes to answer your question.Yes,on HOSE(ha-ha) off hose,in lake,out lake,jet in, jet out. I think I will run on external fuel jug & gravity feed the fuel pump to make sure it is not sucking air,changing carb. base gasket.Had engine out replacing stater,cleaning inside hull,exhaust. Nodes on the fuel vacuum nipple,(turning by hand) wood blow a little,is that a problem? Pumping fuel. Thanks again, slow but sure.

  7. #7
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by sandonut View Post
    ... Nodes on the fuel vacuum nipple,(turning by hand) wood blow a little,is that a problem? Pumping fuel...
    Say what?

    The fuel selector valve must be air tight, as the fuel pump applies mild suction to the fuel feed hoses.

    See this thread;
    Rebuild a Polaris metal Fuel Selector Valve, new o-ring

    If you are referring to the pulse nipple on the side of the crankcase (which powers the fuel pump) that is supposed to provide both pressure and vacuum pulses as the crank rotates.

  8. #8

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    What should the fuel pressure be form fuel pump to carb? My three port fuel pump builds up 5psi at w.o.t. for 4 sec.,One port builds no pressure runs the same w.o.t. rpms dropping 6800,6750,6700,ect.Pop-off pressure has no affect on w.o.t.,right? At what temperature should stater be check at for oms?

  9. #9
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    Quote Originally Posted by sandonut View Post
    What should the fuel pressure be form fuel pump to carb? My three port fuel pump builds up 5psi at w.o.t. for 4 sec., One port builds no pressure runs the same w.o.t. rpms dropping 6800,6750,6700,ect.

    Pop-off pressure has no affect on w.o.t.,right?

    At what temperature should stater be check at for oms?
    Magneto stator coil ohms (if that is what you are asking) should not vary significantly with temperature.

    What do you mean 'one port builds no pressure'?

  10. #10

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    Sorry been so long. One fuel pump has 3 carbs ports that builds 5 psi at w.o.t. for 4 sec. The other fuel pump I have has one carb port for all three carbs that builds no pressure at w.o.t. for 4 sec. The pressure that I am checking is between fuel pump and carbs when at w.o.t. for 4 sec. I ran a vacuum test from carb fuel line back through fuel pump, shut off valve, water separator, leaving the fuel tank out of loop. Plug the hose to the tank. Pulled 24 inch pounds of vacuum for 1 hour, it healed. Hooked gas jug to handle bars, through water separator, shut off valve and fuel pump. Started the engine healed at w.o.t., 6890 rpms with no spark arrestor for as long as I dare, 6780 rpms with spark arrestor as long as I dare, hooked water to the engine 6780 rpms for as long as I dare. I guess the problem is in the fuel tank pick up. I will pull the tank tomorrow to find the problem. Would still like to know pressure between fuel pump and carbs. Will let yawl know what I find in the tank. This sight has helped me a lot with tect info and mere brain whoopee. Thanks a million.

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