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Carb tuning? 1/4 throttle bog

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  • Carb tuning? 1/4 throttle bog

    1998 Polaris SLXH (1050cc) - CDKII (40mm) carbs. Rebuilt by Polaris two days
    ago. SBT carb kits used (THANKS)!

    Ski starts
    and runs great. Idles 1200 in the water, 3000 out of the water. Power is excellent.
    60-62 mph, 6500 rpm tops.

    I'm running it rich currently. 50:1 premix in the tank and the oil injection is hooked up. It's running Yamahalube oil. It's being run rich because it was just cleared after ingesting water via previous owner.

    Problem:
    The ski bogs down at 1/4 throttle. You can't hold the throttle at 1/4, or the ski will die.
    Idle is fine, 1/2+ throttle is fine. This makes the ski a real pain in the *** and rather "zippy".

    Anyway, could the over-rich condition be the cause of this problem or should I be
    looking for something else like vacuum leak or idle speed screws?

  • #2
    Adding oil does not make it rich - adding fuel does. Adding oil to the fuel mix actually leans out the mixture somewhat. You are either fouling the plugs due to the extra oil, or have some damage due to the water ingestion. Exactly what was done directly following the incident? What is the compression reading on each cylinder (read cold)?

    Comment


    • #3
      I'm new to two strokes. I thought that adding oil richened the mixture, but I understand we're talking about air/fuel not oil/fuel.

      Compression on all 3 cylinders is 120-122 psi. Ski was bought at an auction, so I have almost no history on it, other than the fact that someone tore up the bendex trying to start it with water injested.

      I removed the premix today, cleaned the plugs and I'm still having the same issue. Other than 1/4 throttle the ski runs great and I have no complaints.

      Blipping the throttle (using the accelerator pump) cures this problem for a few seconds. Is this an idle adjustment (transition) issue? Any other guesses?

      Comment


      • #4
        Well, if giving it more gas cures it, then I would say you either have the carbs low-circuits set too lean, or have a fuel delivery problem specific to the internals of the carb(s). Your idle speed screw does not effect your mixture, just the amount of thorttle given by default. You should be idleing at 1500 RPM in the water, higher out.

        Try turning your low-speed screws 1/2 turn counter clockwise to give yourself more gas and see if it's better. If it's better, keep turnign out until it's good. If this is the case, then you didn't have a bog, you had a hesitation, a sign of being lean. I swear, I'm just going to have to make a video showing what all these things sound and look like so everyone can get a really clear picture...

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