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  1. #1

    More SLT780 Problems

    Guys....here's the short version (sorta):
    1. Bought 1997 SLT780 with a melted MAG piston.
    2. Did a complete top end rebuild and changed out all of the fuel system. Also converted to premix.
    3. Ran fantastic for about 5 hours.
    4. Started to bog down when you would try to accelerate.
    5. Found bad fuel pump and rebuilt with Mikuni kit this time around.
    6. Runs great on the top end (about 6350RPM/50+MPH).
    7. Started to make a popping sound at low RPM/low throttle. Sorta weird, just a pop here and there and you can feel that it does not have the low end it should. It's not bogging like before, just this popping/missing.
    8. Most of the day today it would clear up once your ran it wide open for a few seconds. On one run, it would not clear up. I came back, looked for obvious things, took it back out and it cleared up again on the top end but was still popping/missing after a few seconds at light throttle. I know it sounds like a fouled plug but the plugs look fine. Certainly not gunked up enough to be fouled.

    Where should I look next? The carbs were rebuilt along with the top end (used an MSW kit....I know...I know).


  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    There's nothing wrong with WSM top end kits at all. Most of us are or have used them.

    First try the cheapest thing. Replace the spark plugs. You should be using NGK BPR8ES

    It clearing out makes me think it's running rich down low. Are your carbs set to factory spec for your year?

    Did you sync the carbs? (all open the same amount at the exact same time)

    Were the carb adj screws damaged at all? (wear marks on the needle tips)

    Is your choke fully open?

    How did the reeds look when you had the carbs off?

    Did you replace the needle and seats?

    Can you see fuel dripping out the carbs when at idle?

    Can you see alot of fuel mist spitting out the carb tops with the FA removed?

    What's your compression?

  3. #3
    Quote Originally Posted by xlint89 View Post
    There's nothing wrong with WSM top end kits at all. Most of us are or have used them.

    First try the cheapest thing. Replace the spark plugs. You should be using NGK BPR8ES
    That's what I am using, they only have about 10 hours on them but I will put new ones in just to be sure.

    It clearing out makes me think it's running rich down low. Are your carbs set to factory spec for your year?
    As far as I know, yes. I used the settings in the Clymer when I rebuilt the carbs.
    Did you sync the carbs? (all open the same amount at the exact same time)
    Well....they visually appear to be in sync but I did not use a manometer (or whatever you call it to do the sync).

    Were the carb adj screws damaged at all? (wear marks on the needle tips)
    No they looked new.

    Is your choke fully open? Yes.

    How did the reeds look when you had the carbs off? Big mistake here. I did not know what I was doing at them time and I did not inspect the reeds (can this be done with the engine in the hull)?

    Did you replace the needle and seats? No. They looked new.

    Can you see fuel dripping out the carbs when at idle? No, not at all.

    Can you see alot of fuel mist spitting out the carb tops with the FA removed? I can't see any spitting out the top but there is a light coat of oil on the top of the FA cover (inside).

    What's your compression?
    MAG105-125-125PTO. I need to recheck as the cross hatch was still visible so I assume the rings are not fully seated.

    I know the 105 is not ideal but it seems high enough that it should still be working. I agree that it seems like it's loading up but visually the plugs look fine. The next time it starts sputtering and popping I am going to shut it off immediately, swap to new plugs and see what affect it has.

  4. #4
    Oh yeah....I meant the carb kit was an MSW (I think), not a genuine Mikuni. The top end kit is MSW but that all looked good. Was told to use genuine Mikuni kits for the carbs. One more question.....you had mentioned that fuel pressure should be 5-6 PSI at wide open throttle and 1-2 PSI at idle. After rebuilding the pump, I was getting 1-2 PSI at idle and about the same when I reved it up (was not in the water so I could not go full throttle). I'll check the pressure under load but does this sound like it could still be a problem?

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