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  • 96 GTX high speed screws

    I finaly got the new needles for my carbs. I went through them again all was clean no trash in the filters. I set both carbs with a pop off of 35 psi, the lows at 1-1/4, highs at 1/4 jets are stock (or at least what came with the ski). It runs strong, puls good, no rough spots, but is down 100 to 200 rpms from what it was with the old engine and it still looks lean on the wot plug chops. I am out to 1/2 turns on the mag and 1-1/4 on the pto highs. The ground electrode is witeish gray and the porcilin has a shiney metalic look to it the rim and metal portion still have a dark brown look to them. What am i missing? Fuel pressure? Do i need to change the high speed jets?

    Thanks, Rod

  • #2
    I would at least verify what jets are installed. Is the ski stock?
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    • #3
      Yes it is stock. I have to think thet the jets are correct as the ski ran fine when i bought it, for at least 25 hours with 24 of that being WOT! Is it possable that rotery valve timing is affecting it? Or maby the raves or water regulator?

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      • #4
        The only thing that can do that is incorrect carb tuing, incorrect carb building, incorrect plugs, an air leak or a restriction in the fuel system.
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        • #5
          Auto line is fine mechanically, it's just hard to get on some skis because it's thicker.

          Another common mistake is people putting the wrong bolts back in the rotary valve cover - there are similar bolts that are 1/4" too long, and when they run them in they crack the mounting surface creating a leak, and/or cracking the case. make sure your cover bolts are not bottomed out.
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          • #6
            Cracking cases on a 787? I thought that only applies to the 720 type motor with the ears on top?

            If he has a stock 787 motor, and he is 1/2 and 1.25 turns out on the highs, he is washing his plugs with fuel, and he will never get the plug color he is looking for. Why open the adjusters to 1.25 when the book calls for closed?

            If it is necessary to open them at all, he has an air leak or fuel is not flowing correctly.

            My suspicion is that he is looking at fairly new plugs and they are lightly colored. He is nervious about it, so he opens the adjusters.

            Any tint of tan or brown is good. It means the air/fuel ratio is within reason. It is not mandatory to see a real dark brown plug. Over time, the plugs will darken more.

            Unless of course, there is a problem with an air leak or fuel flow is interrupted.

            Automotive fuel line works great. It is not larger than oem fuel line if you buy the smaller outside diameter line, sold at hose supply warehouses like HOSEMAN, Mc Master-Carr, ect.

            The on-off-reserve valve may be plugged up. Blow air though it in both positions to check it.
            If you have any automotive type fuel filters installed in the fuel lines, take them out until you find your problem. They may be restricting the fuel flow.

            You have one fuel pump on one carb feeding both carbs. If it is weak, I can see a problem with fuel flow. You could try and a remote Mikuni fuel pump to eliminate that as a problem, or completely rebuild the oem pump.
            Bill O'Neal WCM
            <a href="http://www.watercraftmagic.com" target="_blank">www.watercraftmagic.com</a>

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            • #7
              I was thinking this was a 720...my bad.
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              • #8
                Well i have had some trouble with the carb rebuilding thing ( and a thought the old ford V V"s were tough), but i have looked every over numerous times in the carbs this time. They are spotles inside all the gaskets are in place. all holes open. I guess its time to replace all the fuel lines. When i clean out the filter it pulls fuel almost instantly upon startup though (if that is any indication). The plugs are NGK BR 8 ES which is the spec plug and what kind of air leak could be common to two engines? This is the second SBT. Is there a recomended method of checking for restrictions? Maby a pressure and flow rate thing?

                BTW thanks for the very promp replys (I guess us ski people dont ever sleep :D )

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                • #9
                  On two engines I would suspect a leak at the intake manifold or carb base gaskets, if it's a leak. As for fuel pressure you just have to make sure everything is clean - the lines, fittings, fuel switch, pickups, etc.
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                  • #10
                    Carb base gaskets are new, no old peices on carbs or intake. The intake oring is new again. and i did look it over for cracks, but if i find nothing in the fuel system i will pul it and look again. Is there any reason not to use "quality" automotive fuel line in replacing lines? I figure that if its going to be apart i might as well replace what i can afford to. I guess this does it for me tonight, I will read your reply tomarrow. Thanks again

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                    • #11
                      The plugs come out hot and dry! I dont think they are washed but i will take it out tonight run it hard and take some digital pix to post. The plugs also have about 8 hours on them and had a nice dark brown color on the porclin when i was checking the mid range. The fuel pump had every thing that comes in the SBT kit installed in it. I do find it odd that I was not having problems with the old engine set up and now I do. So i am not beyond saying its some thing I did, i just dont know what it was.

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                      • #12
                        I'm really leaning towards an incorrect carb build - it's easy to make mistakes if you aren't sure what to look for.
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                        • #13
                          Thats posable i guess, but I've been through them like 6 times. The jets have been out twice and cleaned along with the passages. the valve body has no cracks and the anti bleed valve is new and over the hole. The needles are new(old seats). the high and low speed screws look good and their passages are clean. The filters are clean. I went back to the mikuni diaphragm. The pop-offs we set to 35 psig as indicated by and NH3 rated glycerin filled gage (I know its accurate). The fuel pump portion is the only part that was only done once. So I will check it again. Whats left in the carbs? To be so friggen complex there realy isnt that much to them. I still have not checked the fuel delivery system or the intake yet but I will.

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                          • #14
                            The fuel pump gasket order and condition is the side I would suspect.
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                            • #15
                              will tear it down and look thanks

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