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SBN 44 Pop Off Pressure Advice

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  • #1

    SBN 44 Pop Off Pressure Advice

    I have a clean 1998 Yamaha 1200. Replaced SBT engine due to #3 Scoring. In process of rebuilding Mikuni SBN44 Carbs to Factory specs. Installed new 1.2 NS, cleaned carbs, and installed SBT carb kits. Used original springs. Tested Pop off with new tool purchased SBT. Found Carb 1 - 32psi but doesnt pop off good more of a spew and doesnt close well. Carb 2 - 40 psi pop off acts like a slow leaker. Carb 3 - 45 psi and not a good pop more like a slow leaker. Per Yamaha service manual the carbs I have came with 1.2 needle and seat, main jet 135. Pilot jet in Carb 1-100, Carb 2-95, Carb 3-97.5. Which I checked and verified is the same setup I have currently. This is the first time carbs have been rebuilt and they have no corrosion.

    1.What should I shoot for on the Pop Off pressure
    2.Why are the new needles and seats not acting right?

    NEED RECOMENDATIIONS PLEASE. Been trying to get ski on the water for over a month. Bummer

    Thanks
    Last edited by elcidkid79; 07-31-2012, 07:45 PM.
    Tags: None
  • #2
    Re: SBN 44 Pop Off Pressure Advice

    45-50 on pop-off, remove the fuel pump and go through the fuel filter port to do your pop-off check.
    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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    • #3
      Re: SBN 44 Pop Off Pressure Advice

      I wish I could check thru the fuel filter port as your instructions show however your SBT Tester does not come with an adapter. Merely a 1/4" piece of hose that doesn't even fit the 3/16" fuel inlet on the Mikuni carb. I called SBT tech services after receiving tester and they told me to hook up to fuel inlet? I too was surprised the pressure tester did not have a adapter for testing thru the fuel filter port.

      Please tell me how to proceed? Based on the lack of a consistent "Pop" I suspect the needle and seat are bad from SBT? I am very frustrated at this point that I can't test as recommended. I do not want to loose another engine due to a carb issue. Please help!
      Last edited by elcidkid79; 08-01-2012, 08:24 PM.

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      • #4
        Re: SBN 44 Pop Off Pressure Advice

        Most of the testers dont come with the adapter, Let me try to locate 1 for you.
        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: SBN 44 Pop Off Pressure Advice

          That sure would be great if you can offer the adapter. Thanks

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          • #6
            Re: SBN 44 Pop Off Pressure Advice

            Its seems no one offers the adapter from the old style thumb pump any more. Try sealing up the fuel pump better and try to get it to work through the fuel inlet.
            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.

            Comment

            • #7
              Re: SBN 44 Pop Off Pressure Advice

              I did as you said, tightened up fuel pump side. Pressurized each carb, changed springs, and set pop off at 50 psi. None of the carbs pop off but more of a bleed off. Reinstalled carbs. Took to lake and now the engine will not start. You can prime the engine and get it to start for a second. Changed spark plugs, still not starting. I guess I will have remove carbs and start over but feel like its in the new needle and seat since it appears I am not getting fuel? Double checked everything else like low speed adjustment. Already had replaced fuel lines and reed valves when installing new engine.. Got any ideas?

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              • #8
                Re: SBN 44 Pop Off Pressure Advice

                Double check your fuel line routing.
                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.

                Comment

                • #9
                  Re: SBN 44 Pop Off Pressure Advice

                  Hi I have the exact same ski with the same problem,i bought the SBT carb kits and the 1.2 needles from SBT and had the same issues as you, aparently the 1.2 needle and seat from SBT are faulty SBT is aware of this, i had bad pop off psi anywear from 32-45 psi with the sbt needles,i had to purchase them from yamaha,after i installed them my pop off was 65 psi with no problems.
                  I also had a problem with the SBT carb rebuild kits my fuel pump was leaking down and you chould see the leak between sections after pressurizing and applying WD40 around the pump sections.so i had to purchase the gaskets from Yamaha and know the ski runs perfect.
                  hope this helps

                  Comment

                  • #10
                    Re: SBN 44 Pop Off Pressure Advice

                    We did have a batch of not so good needle and seats for yamaha replacements, did you get them from SBT and if so how long ago?
                    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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                    • #11
                      Re: SBN 44 Pop Off Pressure Advice

                      Kevin,

                      Thanks for that information about SBT carb kits. I have had the same trouble with pressure leaks on regulator side! I asked SBT to replace the kits which they kindly provided at no charge yet had the same results, leaks and sticky needle and seat. I will try going thru Yamaha and hopefully get higher quality parts. It is so frustrating to rebuild your carbs, go to the lake and they don't work. Go back home and remove carbs, try again. I have alot of hours removing and reinstalling carbs. Like they used to say about computers....garbage in garbage out.
                      Last edited by elcidkid79; 08-16-2012, 09:34 AM.

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                      • #12
                        Re: SBN 44 Pop Off Pressure Advice

                        I just purchased a new engine and carb kits in June 2012. As well as 1.2 needle and seats. I also had regulator side leaks after rebuilding carbs. This caused problems trying to test pop off pressure since we can't test thru fuel filter port because SBT pressure pump gauge doesn't come with adapter like it shows with carb kit rebuild instructions. Need to either change instructions, offer adapter, or use better regulator gaskets.

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                        • #13
                          Re: SBN 44 Pop Off Pressure Advice

                          The reason why the 1/4" fuel line won't stay on is because yamaha uses 5mm fuel lines which is about impossible to find in the us.I bought a roll of 1/4 from Sbt last year to replace my old lines and I had leak problems and had trouble finding clamps that small since zipties wouldn't work either.I ended up finding some 3/16" similar hose which is made by parts unlimited and is actually 4.7mm and with the help of a little windex they slide on nice and tight.***********ATTN sbt you should really consider stocking 3/16 or 5mm,hose since the 1/4" is slightly larger and doesn't seal properly,and is very dangerous since the hull can fill with fumes and explode.my fuel leak wasnt noticable unless the ski was running under load in the water and since there was a little water in the hull,it was hard to see that it was a fuel leak

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                          • #14
                            Re: SBN 44 Pop Off Pressure Advice

                            stainless 1/4" screw type hose clamps hold the hose on tight without any leaking issues, they can be purchased at any automotive parts store.
                            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.

                            Comment

                            • #15
                              Re: SBN 44 Pop Off Pressure Advice

                              I tried the screw clamps from autozone with no luck since the
                              1/4" clamps are designed to be used with thicker rubber hose,plus they arent stainless so corrosion is a factor,besides you want the hose to fit snugly over the nipple and seal at the nipple,you are never supposed to use a clamp to seal a hose,the hose needs to fit properly.

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