1992 750sx 44 SBN mikuni jetting with factory pipe - Page 3
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  1. #21
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    Re: 1992 750sx 44 SBN mikuni jetting with factory pipe

    Water in the exhaust is probably not the problem. I would tee the stinger line to a large pisser, that will keep excess water out of the exhaust.
    What exactly does the IJSBA do?

  2. #22
    PWCToday.com Is My Home Away From Home fastgtfairlane's Avatar
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    Re: 1992 750sx 44 SBN mikuni jetting with factory pipe

    How do you have your water routing setup? I run a dedicated cooling line to the bottom of the headpipe from the pump to better control the pipe temps and it also puts more pressure on the injector holes for a better spray pattern. On the outlet run a tee to a flow control valve to the stinger. On the other side of the tee, run to a pisser with a small restrictor in the pisser line. This helps keep a little pressure on the control valve so it will open up. The flow control valve just keeps the water box dry until the ski gets on a plane and it should start opening up.
    96 superjet- rockered, -4, wide tray, adjustable footholds, kv148 mag setback pump, skat 7/14 impeller, rrp adjustable pole, blowsion ovp steering, 62t/62t, ada head, zeel A02T cdi, dual 44s, boysen power reeds, TNT SS chamber

    93-x2, newmiller ported SP750, milled head, R&D single 46 intake, sbn46, fpp blaster chamber pipe, hooker 9/15, umi, rhaas squirrel cage, dakine foot straps

  3. #23
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    Re: 1992 750sx 44 SBN mikuni jetting with factory pipe

    So i ran a tee between the cylinder head and headpipe to a pisser to decrease water to the pipe and waterbox. Worked wonders! Boat ran way better. Power is better throughout rpm range. Still hesitates at the bottom coming out of the hole. I decided to take the hood off and test it like that. Just a split second of hesitation but much better. So help me out here guys. What do you think? Here’s an A/B video with hood on and off.
    Last edited by Thorny; 12-05-2021 at 04:56 PM.

  4. #24
    PWCToday.com Is My Home Away From Home fastgtfairlane's Avatar
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    Re: 1992 750sx 44 SBN mikuni jetting with factory pipe

    You dont want to decrease the water flow to the headpipe, just to the stinger. What carb settings are you running in the last video?
    96 superjet- rockered, -4, wide tray, adjustable footholds, kv148 mag setback pump, skat 7/14 impeller, rrp adjustable pole, blowsion ovp steering, 62t/62t, ada head, zeel A02T cdi, dual 44s, boysen power reeds, TNT SS chamber

    93-x2, newmiller ported SP750, milled head, R&D single 46 intake, sbn46, fpp blaster chamber pipe, hooker 9/15, umi, rhaas squirrel cage, dakine foot straps

  5. #25
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    Re: 1992 750sx 44 SBN mikuni jetting with factory pipe

    Quote Originally Posted by fastgtfairlane View Post
    You dont want to decrease the water flow to the headpipe, just to the stinger. What carb settings are you running in the last video?
    150H 120L 2.5 N/S 80 gram spring. 1 turn out low. 1-1/4 high. I tried running a flow control valve before the stinger to reduce water. Didn’t really help.
    Last edited by Thorny; 12-05-2021 at 05:35 PM.

  6. #26
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    Re: 1992 750sx 44 SBN mikuni jetting with factory pipe

    E49D325D-B2EF-4D58-A3AC-D2907B1B2543.jpeg
    Quote Originally Posted by fastgtfairlane View Post
    How do you have your water routing setup? I run a dedicated cooling line to the bottom of the headpipe from the pump to better control the pipe temps and it also puts more pressure on the injector holes for a better spray pattern. On the outlet run a tee to a flow control valve to the stinger. On the other side of the tee, run to a pisser with a small restrictor in the pisser line. This helps keep a little pressure on the control valve so it will open up. The flow control valve just keeps the water box dry until the ski gets on a plane and it should start opening up.
    Before I made the change today I had the line from the pump to the factory exhaust manifold then out of the cylinder head to the top fitting on the headpipe, then out of fitting on bottom of headpipe to a tee. Out of bottom of tee to stinger, out the other side of tee to front of hull oversize pisser. I have also tried it with flow control between bottom of tee to stinger (red circle in pic)
    Last edited by Thorny; 12-05-2021 at 05:52 PM.

  7. #27
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    Re: 1992 750sx 44 SBN mikuni jetting with factory pipe


  8. #28
    PWCToday.com Is My Home Away From Home fastgtfairlane's Avatar
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    Re: 1992 750sx 44 SBN mikuni jetting with factory pipe

    2.5 n/s with 80g spring is around 14psi popoff. That's really low which makes your jetting richer. If you dont have a 2.0 n/s, try a 115g spring. Should be stiffest and has extra ring on top and bottom. It should give you around 19psi which is closer to where you need to be. 95g spring should get you around 17psi which might work too. 95g spring is reverse wound. Leave everything else the same. Your plug readings look almost wet like excessive fuel wash but that is almost impossible to tell through pics.
    Last edited by fastgtfairlane; 12-05-2021 at 08:31 PM.
    96 superjet- rockered, -4, wide tray, adjustable footholds, kv148 mag setback pump, skat 7/14 impeller, rrp adjustable pole, blowsion ovp steering, 62t/62t, ada head, zeel A02T cdi, dual 44s, boysen power reeds, TNT SS chamber

    93-x2, newmiller ported SP750, milled head, R&D single 46 intake, sbn46, fpp blaster chamber pipe, hooker 9/15, umi, rhaas squirrel cage, dakine foot straps

  9. #29
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    Re: 1992 750sx 44 SBN mikuni jetting with factory pipe

    Quote Originally Posted by fastgtfairlane View Post
    2.5 n/s with 80g spring is around 14psi popoff. That's really low which makes your jetting richer. If you dont have a 2.0 n/s, try a 115g spring. Should be stiffest and has extra ring on top and bottom. It should give you around 19psi which is closer to where you need to be. 95g spring should get you around 17psi which might work too. 95g spring is reverse wound. Leave everything else the same. Your plug readings look almost wet like excessive fuel wash but that is almost impossible to tell through pics.
    Ok I’ll give it a go. Thank you

  10. #30
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    Re: 1992 750sx 44 SBN mikuni jetting with factory pipe

    Quote Originally Posted by fastgtfairlane View Post
    2.5 n/s with 80g spring is around 14psi popoff. That's really low which makes your jetting richer. If you dont have a 2.0 n/s, try a 115g spring. Should be stiffest and has extra ring on top and bottom. It should give you around 19psi which is closer to where you need to be. 95g spring should get you around 17psi which might work too. 95g spring is reverse wound. Leave everything else the same. Your plug readings look almost wet like excessive fuel wash but that is almost impossible to tell through pics.
    I have a 2.3 n/s and a 95 spring handy. What do you think? That should be around 20 psi pop off.
    Last edited by Thorny; 12-06-2021 at 11:16 AM.

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