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98 GP1200 Carb Tuning

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  • #1

    98 GP1200 Carb Tuning

    Ok, I have 2 of these skis and I rebuilt the carbs in both. (One has a new SBT motor in it :) ) Now, I've set the hi/low speed jets to match the specs in book. They are both doing the same exact thing. While testing these on the hose, they both have the top of the f/a off so I can view oil flow. I'm not sure if the extra air getting in has an impact?

    Question 1: How far do the jets have to screwed in before I count the turn out. I turn them in as far as the black tabs on the outside allow me, but if I wanted to, I could force them in further, prior to turn out?

    Question 2: Both purr like kittens when I start them up and idle for 5 minutes on hose. If I give them throttle they sound great until the transition to high speed (3k-4k rpm) then they sound garbled for a second or so then sound great at 6k-7k rpm. Turning the high speed screws in/out seemed to make no difference.

    Question 3: After about 7 minutes of the hose, the rpms drop from 2700-3000 to 1000-1500 ?

    Question 4: I was watching the carbs on one of the skis, I'm relatively new to how these things function, does the gas drip out of the center of the carb? It looks like it to me. And the oil dribbles down the side. I ask this about the gas, because it looked like my mag cylinder was not getting any gas if that's the case....

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  • #2
    Re: 98 GP1200 Carb Tuning

    At idle, you should not see any gas dribbling out of the "bulls eyes" in the center of each carb. Please provide the specifics of what you used when you rebuilt the carbs (sizes of N/S, popoff spring, low jet, high jet).

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    • #3
      Re: 98 GP1200 Carb Tuning

      I used Mikuni rebuilt kits and the same stock spring/needle/seat/hi&low jets. Very small dribble..

      Also, I got the carbs set up properly on my ski with the new SBT motor. I went out and broke in the first 10 gallons. Everything went perfectly, I followed SBTs break in instructions.

      NOW, when I was done and flushing out the ski with the hose...The idle was at 3-4k...Before, on the hose, prior to riding, it was at 2500-3k. I turned the idle control and lowered the rpms appropriately and 30 seconds later, I had engine runaway....I covered the exhaust and stalled it, what the hell is going on!?!

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      • #4
        Re: 98 GP1200 Carb Tuning

        How long were you idling before it ran away? Was it on the hose the whole time?
        SBT Tech Support is here to help with your problems.
        We try to answer each question quickly and accurately.
        Please do not use Private Messaging for Tech Support, use the forums.

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        • #5
          Re: 98 GP1200 Carb Tuning

          Was idling for a minute or so, the idle was high at 3-4k so I turned the idle screw out slightly until it got in the 2500-3k range. Then about 30 seconds later, it ran away for maybe 4-5 seconds until I stalled it, on the hose the whole time.

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          • #6
            Re: 98 GP1200 Carb Tuning

            Definitely sounds like a carb issue... possibly a N/S not seating properly (??). Its always a good idea when you rebuild the carbs to go ahead and replace the N/S's as well.

            Many (including myself) have also increased from the 95-g to the 115-g springs to get rid of the dribble.

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            • #7
              Re: 98 GP1200 Carb Tuning

              A leaking N&S will never cause a runaway. If you were on the hose when it did it, it is either one or more carbs way too lean on the bottom end, and/or an air leak.
              SBT Tech Support is here to help with your problems.
              We try to answer each question quickly and accurately.
              Please do not use Private Messaging for Tech Support, use the forums.

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              • #8
                Re: 98 GP1200 Carb Tuning

                :D I had a sneaking supsicion it might be an air leak, I checked, and sure enough, I found a pulse line from the pto carb to the engine that was coming loose...I'll let you know if I experience the same problem after the fix..thanks!

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                • #9
                  Re: 98 GP1200 Carb Tuning

                  Did you forget to put clamps or zip ties on all your lines?
                  SBT Tech Support is here to help with your problems.
                  We try to answer each question quickly and accurately.
                  Please do not use Private Messaging for Tech Support, use the forums.

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                  • #10
                    Re: 98 GP1200 Carb Tuning

                    No no no...On the one line I'm referring to, it has a hairline tear on one end that go much further up the pipe than I though when I inspected it. The tear goes well beyond the zip tie and above the nipple the hose goes on...Is that probably it?

                    Actually, come to think of it, this exact nipple is the one that fell out when I first got the engine, the press fit one with the green loctite...still probably the hose though.

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                    • #11
                      Re: 98 GP1200 Carb Tuning

                      Ah gotcha. That will cause an air leak into the engine and it will prevent that carb from pumping fuel properly, leaning that cylinder out.
                      SBT Tech Support is here to help with your problems.
                      We try to answer each question quickly and accurately.
                      Please do not use Private Messaging for Tech Support, use the forums.

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                      • #12
                        Re: 98 GP1200 Carb Tuning

                        So 99% sure that's the problem? Ran fine on the water all day, it would do that?

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                        • #13
                          Re: 98 GP1200 Carb Tuning

                          I don't know if that's your ONLY problem, but I'm 100% sure that will cause the conditions I mentioned.
                          SBT Tech Support is here to help with your problems.
                          We try to answer each question quickly and accurately.
                          Please do not use Private Messaging for Tech Support, use the forums.

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                          • #14
                            Re: 98 GP1200 Carb Tuning

                            Cool, I'm sure that's what caused it, thanks for your help.

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                            • #15
                              Re: 98 GP1200 Carb Tuning

                              Tech support is correct.. run-on is usually caused by a lean condition not a rich fuel condition. my error.

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