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  1. #1

    Help: SLT 780 falls on face coming off the throttle.

    Hey guys. First post on the site, but Iíve used it for a couple years for research. Last year I got a 1998(maybe 1997) Polaris slt 780. When I got it the mag side
    piston was cooked. I went one size over on just that cylinder as it was scared and the other two holes looked new. Ski has 80hrs. When I pulled it apart it showed that the mag carb was completely plugged off with gummed up fuel which created Lean burn. The previous
    owner told me his son took it out after it
    had sat for a few years then it just wouldnít run right. So this all makes sense to me.

    I got it running and it runs strong, other than it will die out around 2000-3000rpm. I can pull the choke quick and it will keep running or if I let it die it will fire up again(maybe a quick choke some time). So Iím pretty sure itís a
    fuel issue. I pulled the carbs off twice now, but havenít ordered new carb kits, just cleaned them. I know this could be my issue but before ordering $150 in carb kits I just wanted some help with possible tuning? I put a new fuel pump on and it still does it. I set the high and low carbs to the specs I got off this site. Maybe my low needs adjusting? Any help would be mint. Thanks.

  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Welcome to the Hulk.

    Contact John Zigler for GENUINE Mikuni carb rebuild kits. He owns both Rock County Jet Ski and Watcon

    https://rockcountyjetski.webs.com/

    I wouldn't ride that ski until you rebuild the carbs. You risk burning the pistons down again.

    Anytime using the choke helps, you are too lean on fuel.

    FYI: the 780 has a very good fuel pump. You can buy rebuild kits for it very cheap. What fuel pump did you buy?

  3. #3
    I’m in Canada. The mikuni rebuilds are hard to come by here. Everyone wants to sell me Vertex Winderosa kits and everything I read on here tells me to only buy mikuni. I found a set that would be $300CAD which is mayhem. I mean if I knew 100% that it was a sure fix, I’d do it. I bypassed the fuel selector last night and did new fuel lines from the tank, set the high and low adjustments to spec and took it for a drive. Still does the same thing. If I take off and get it going and keep it over 1/4 throttle, it runs great. I can go forever without it dieing. But if I let off the throttle too much it dies. It’s not like I need to drive with the choke on, just a quick pull of the lever and it takes back off again. I would agree it’s a fuel issue, but would think if it was the carb needing rebuilt it would have more of a issue running no? It’s getting fuel at half throttle to full throttle. No one has any other ideas other than buying the $300 mikuni carb kits and hoping that’s the issue? Or maybe someone has some theory of what’s not working in the carb and why this is happening, to give me some knowledge of why I need to rebuild the carb. I want to wrap my head around what’s going on before I just buy $300 carb kit.

  4. #4
    Click avatar for tech links/info K447's Avatar
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    Watcon sells the proper carb rebuild kits and can ship to Canada. Might take a week or two to arrive.

    Where are you finding $300 CAD pricing for the genuine Mikuni Polaris carb kits?

  5. #5
    Myself's Avatar
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    I've used Winderosa kits a hundred times, never had an issue. They probably do need kits based on age alone. Try turning all 3 low screws out an additional 1/4 turn. It should clear right up.

  6. #6
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    There are many circuits that make up the fuel supplied with these carbs. Idle speed screw, pop off pressure, transition ports, low speed jet, high speed jet, and high speed adjustment screw.

    Generally rebuilding the carbs addresses all of these circuits when done properly. So you normally correct whatever the issue is by doing it.

    If you want to dissect every one of the circuits to find exactly which one is failing you, here's the manual in post #7.

    http://greenhulk.net/forums/showthread.php?t=15433

    Also make sure your carbs are all in sync


  7. #7
    Thanks for the reply. I went with a set of winderosa carb rebuilds but as i assumed, it did not correct the issue. I had it out and tried fiddling with both high and low set screws but didn’t have enough time. I’m going to set the highs and lows to the recommended set points then I’ll try your suggestion of dialing the lows out 1/4, thank you. Also maybe I’m shooting myself in the foot here, but I premixed then tank with some oil. I always do this when rebuilding a new machine to me for the reason of not trusting an oil injection pump. Maybe too much oil is causing my issue? If it were the case, I would think it would be bogging out or feeling real loaded up. I’ve never had that make an issue before on anything, but also never had a triple pwc before.

  8. #8
    Quote Originally Posted by Myself View Post
    I've used Winderosa kits a hundred times, never had an issue. They probably do need kits based on age alone. Try turning all 3 low screws out an additional 1/4 turn. It should clear right up.
    would the cylinder that I went one size over on, need more fuel than the recommended settings you think? Or not enough size difference to require an upped fuel setting?

  9. #9
    Myself's Avatar
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    Nothing more than a screw adjustment at most.

  10. #10
    Quote Originally Posted by Myself View Post
    Nothing more than a screw adjustment at most.
    sadly not the case. Took it out tonight. Went basically a full turn out in 1/4 turn increments and no luck. Set it back to stock recommendation and tried going in without luck also. Going out maybe made it slightly better. If I feather it to take off it just bogs out and almost ride down. If I hit it and hold it it will die. If I pull the choke and push it in as quick as possible it will take off just fine until I let off down to the 2200rpm area. Kinda scratching my head. Just checked and all 3 holes have 130ish lbs compression. Has to be a fuel issue but not sure where. Im gonna pull the fuel tank and add new straight fuel(no premix) and check the fuel pickup in the tank. Anyone else have any ideas that I’m missing. I’ve read the whole website and can’t seem to find my answer.

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