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  1. #1

    SLT 780 top speed problem

    Can anyone tell me why my 97 polaris SLT 780 suddenly rockets from 38 mph at full throttle to top speed (55/58 mph) and full rpm after hitting a few well timed waves. This seems to be the only way to achieve top performance / speed. Once I get it to top rpm / speed I can stay there indefinitely. However, 40 mph is as fast as I can get it to go once I back off the throttle until I hit a few good waves again. This type of behavior doesn't seem to be remedied or consistant with simple carb adjustments (but maybe I'm wrong). I did a cold compression check (all in the low 120's) . This ski runs smooth low to midrange and idles well. Might not pull out of the water as fast as I'd like it to, but maybe that is also part and partial to its "top speed challenge". I'm not sure as I'm new to this ski. This ski is completely stock and all original including fuel lines. I have noticed that the fuel/water separator never completely fills. (is this normal?) Also, this ski seems to use a lot of fuel. Any suggestions are really appreciated. - Bobby

  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
    Join Date
    Oct 2006
    Cleveland OH
    Welcome to the Hulk Bobby.

    It sounds as if you're not running on all 3 cyls all the time.

    1. the water seperator should be full of fuel. (the orange ring isn't floating is it?)

    2. Those skis really are fuel economical

    First, try removing the spark plug boots, cutting about 1/4" of wire off to expose fresh wire. Then rescrew the boots back on and zip tie them in place. (sometimes the connection gets bad and you lose spark)

    Read up on "piston wash" and compare yours to a good wash pattern.

    Lastly, I had a similar situation with the high speed coming on after hitting waves, and that turned out to be my elec stator/magneto. So make sure all your electrical connections are good, clean, and tight. Especially the ground wire connections.

    This thread should help point you towards some things to look into. What you need to know about Polaris 650 750 780 785's

  3. #3
    Wow, hey thanks for your help. I'll do as you suggest.
    and, the orange ring is not floating. So, I assume tightening the connections is in order? - Bobby

  4. #4
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
    Join Date
    Oct 2006
    Cleveland OH
    Not just tightening. Make sure the terminals and contacts are clean too.

    Ring not floating is good. Not sure why your water seperator isn't filling all the way though. You may want to inspect ALL your hoses and connections for any type of leaks or possible air leaks INTO the fuel system.

    Once again, get a good look at your piston wash as that will indicate if you're running out of fuel, or if you're getting too much

  5. #5

    Join Date
    Sep 2011
    Lynden wa
    Did you get this figured out? I have the same problem. The only thing I haven't tried yet is a new stator.

  6. #6
    Just my 2 cents but I had a simular prob and cheched everything possible and finnally found problem after running it with air filter off ,,let me recap problem ,,run rough ,,sometimes great, low rpms some time,, bogging after 360's,, and then great,,anyway I had a broken reed valve and only saw it after i ran it at my shop with water connected with air filter off ,,one cylinder was kinda spitting back up gasoline vapors though carb!
    took it apart checked everything and found a broken reed valve !!
    replaced it and put it back to gether and works great
    I'm though a lot of things were the cause but when i ran it without the upper air filter in place i saw the culprit
    Good Luck on finding your problem ,,
    but if your fuel seperator doesnt fill check fuel pump and hoses first

  7. #7
    Okay, lets see.. I've rebuilt carbs to spec (including checking pop off), installed new fuel lines, compression is good on all three cylinders, rebuilt fuel pump, and checked ventilation check valves, new plug wires.
    However, now all it takes to get to top end speed/rpm is a good hard right turn at midrange speed then off she goes rocketing to a smooth at 55 / 60 MPH.
    Any suggestions about fuel intake/sending unit. Repair manual says that there is no sort of "turn over check valve" inside the fuel tank. Does anyone have experience with intake sending unit problems as it might relate to fuel delivery? I cringe at the thought of having to take to fuel tank out...looks like a pain in the butt. Additional Multi Function Display is disconnected...but I doubt that would have anything to with not being able to achieve top end speed at WOT (such as rev limiter interfering) because I can achieve top end revs after a hard right turn. It was mentioned that the stator might be the culprit…but that doesn’t seem consistent with it behavior either

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