Addendum to the Mikuni SBN Tuning Manual - Page 8
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  1. #71
    PWCToday Newbie
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    Re: Addendum to the Mikuni SBN Tuning Manual

    Well good news is I have plenty of spare Jets now, a boat load of springs in each weight and spare NVs too. Oh and a notepad filling up with what doesn’t work. So glad I read your post as it gives me a little more structure to go back and retest each time and identify where the problem is occurring. Will keep at it. Thanks again for your OP and your quick reply to my question.

  2. #72
    PWCToday.com Is My Home Away From Home john zigler's Avatar
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    Re: Addendum to the Mikuni SBN Tuning Manual

    Quote Originally Posted by Klong View Post
    Well good news is I have plenty of spare Jets now, a boat load of springs in each weight and spare NVs too. Oh and a notepad filling up with what doesn’t work. So glad I read your post as it gives me a little more structure to go back and retest each time and identify where the problem is occurring. Will keep at it. Thanks again for your OP and your quick reply to my question.
    You want to run a small of a needle / seat as possible to achieve desired pop off.

    Go back to 1.5's (Get NEW) Going by memory I think you want 65 gram springs. Try 70 pilots, and 150 mains. Make sure you are using GENUINE mikuni needle and seats, and springs.
    RCJS also doing business as WATCON
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  3. #73
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    Re: Addendum to the Mikuni SBN Tuning Manual

    I've heard the thing about using the smallest seat on the needle and seat as possible before. What is the reason for that?

  4. #74
    PWCToday.com Is My Home Away From Home fox river pwc's Avatar
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    Re: Addendum to the Mikuni SBN Tuning Manual

    As the SBN manual states, the 1.5 is all the SBN can pump anyhow.

    I've had a few situations where the 65gm spring isn't stiff enough to stop a dribble at idle, so then I've swapped to the next size larger seat and gone with a stiffer spring to solve that issue.

    Screenshot_20220809-092410_Gmail.jpg
    Last edited by fox river pwc; Today at 10:28 AM.


    WHEN IN DOUBT, GAS IT!

    Yeah, I'm an @sshole, but I'm not a complete @sshole.

    http://badgerlandjetpilots.com/

    I don't come here to make enemies - only to identify them...

  5. #75
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    Re: Addendum to the Mikuni SBN Tuning Manual

    Thanks John, I did try to keep the NV/seat as small as possible per the Mikuni manual. However I found the 65gspring too light to overcome the vibration. So I went with the 115g on a 2.0 to give me the same POP off with a heavier spring. Working well for now but as mentioned I have a rich gargle at around 1/4 throttle. Based on advice so far and what I have tried previously l will go back to 1.5 and 80g and increase Pilot Jet to see if that solves it. Thanks for input. I thought about calling you for a jetting recommendation!!

  6. #76
    PWCToday.com Is My Home Away From Home fox river pwc's Avatar
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    Re: Addendum to the Mikuni SBN Tuning Manual

    With pop off, my primary concerns (in order of concern) are:
    Will it pass a pop off test without leaking?
    Does it remain closed (not dribble) at idle?
    Am I getting the pop off number I am aiming for?


    Pop off can get crazy over-complicated, IMHO, so I try to keep it simple...and like I have stated earlier, it is generally easier to detect a pop off that is too high versus one that is too low - so keep that in mind.

    Fun story: My old vintage race SN was running dual 44 red tops on jet works ported 61x cases and a race ported cylinder. I had issues where it would lean stall about 1 out of 3 or 4 times during holeshots...right as I grabbed WOT when the band snapped. Lots of testing found that it liked 11psi with the pop off actuator arms bent upwards .006" (use a feeler gauge to measure)...that did the trick, lol...stupid amount of work for $13 plaques


    WHEN IN DOUBT, GAS IT!

    Yeah, I'm an @sshole, but I'm not a complete @sshole.

    http://badgerlandjetpilots.com/

    I don't come here to make enemies - only to identify them...

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