Addendum to the Mikuni SBN Tuning Manual - Page 8
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  1. #71
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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; 08-09-2022 at 10:28 AM.


    WHEN IN DOUBT, GAS IT!

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  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/

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  7. #77
    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 Storbeck View Post
    I've heard the thing about using the smallest seat on the needle and seat as possible before. What is the reason for that?
    Larger needle and seats can be more prone to "dribble".
    RCJS also doing business as WATCON
    608-743-1305 9am to 5pm CST m-f
    email watcon@watcon.com

    Please visit our web site

    new parts / products / services www.watcon.com
    thank you

    Please check out and like WATCON on Facebook

  8. #78
    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

    Quote Originally Posted by fox river pwc View Post
    The RN I finished tuning yesterday got picked up last night, and I'm expecting a ride report from the owner after he rides it today.

    And now I have a modded 2016 RN in its place to evaluate and tune. Might get started on it this weekend. Got some family plans this aft/eve, and I really wanna go jump some boat wakes at my place today on my Apex. Bunch of my neighbors will be out plowing , gotta chase wakes when the chasin is good....
    Spent time on/with the 2016 RN today.
    701, girdled head, b-pipe, 38s with aftermarket FAs.
    First issue I noticed was the aftermarket t-handle adjusters, 2 of them, were not able to bottom out due to the t-handles hitting on the carb bodies = not cut down enough.
    Fixed that first.
    Then I started with the lo adjs at 1 and hi adjs at 3/4.
    Best idle had lows at 7/8.
    1/4 to WOT test had a significant gargle that felt like mains to me... came on slightly after stabbing the throttle.
    Taking the highs down to 3/4 was better, but not perfect.
    Highs down to 1/2 even better, but still a gargle.
    Highs down to 3/8 almost got rid of the gargle, but not quite.

    At the same time doing a 5 second true idle and then stab it test caused a lean stall with the lows at 3/4. Was better at 7/8, but that just exaggerated the gargle during the 1/4 to WOT test.

    At that point I said to myself, this thing feels like it has 140 mains in it.
    Keep in mind the owner bought the ski "modded" and had no idea how it was jetted.

    So I pulled the cover on the rear carb just now.
    Sure enough, it has 140 mains.
    Next step is to drop down to 135 mains and test again.
    Will probably start the next test with the lows at 7/8 or 1 and the highs at 3/4.
    Last edited by fox river pwc; 08-12-2022 at 09:31 PM.


    WHEN IN DOUBT, GAS IT!

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  9. #79
    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

    So this 2016 RN is a good example of using the low adjusters...and notes...and careful consideration.

    Started with:
    140 mains
    75 pilots
    Had a gargle under acceleration that turning in both adjusters would improve, but not get rid of.

    Rejected to:
    135 mains
    75 pilots
    Lo adjusters at 1 to start
    Hi adjusters at 3/4 to start

    Better but still a gargle.
    Much testing and noting.
    Dropping the hi adjusters to 1/2 almost gets rid of the gargle, but.....(more in a bit).
    Dropping the lo adjusters to 3/4 gets rid of the acceleration gargle almost completely, but trying the idle to WOT test causes a lean stall.
    Lo adjusters at 7/8 is exaggerated the gargle, and it still likes to lean stall off idle.
    Lo adjusters to 1 fixes the lean stall off idle, but way too much gargle.

    What does this tell us?
    That the motor "likes" the low adjusters at probably 1 to 1.25 turns, but the 75 pilots are too much to be happy combined with that.

    Also, running the hi adjusters at 1/2 is too lean according to what the piston wash is saying.

    So now what?
    Drop the pilots - planning on 67.5, so I can then richen the lo adjusters to what the motor likes off idle, and so I can also richen the hi adjusters to bring back some additional piston wash.

    No fun riding on this one yet. Just thinking
    Last edited by fox river pwc; 08-13-2022 at 10:15 PM.


    WHEN IN DOUBT, GAS IT!

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

    http://badgerlandjetpilots.com/

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  10. #80
    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

    2016 RN update:

    My actual notes:
    Currently jetted as 135 mains and 67.5 pilots. Low adjusters at 1.25, highs at 5/8. Was originally jetted at 140 mains, 75 pilots, and was gargly everywhere, unless you had the hi adjusters at 3/8, and then the piston wash was gone. Dropping to 135 mains helped to allow the hi adjusters to be open to 1/2, but was still very gargly off 1/4 and 1/2 throttle and still not enough wash. Dropped the pilots to 67.5, and this allowed me to open hi and lo adjusters, while keeping the gargle away and getting some wash back - just need to ride more and check the wash. Currently the low adjusters are at 1.25 and hi adjs are at 5/8...idle to WOT is strong, 1/4 to WOT is strong with barely a hint of gargle. Low adjusters "could" work fine at 1-1/8 - would sometimes hesitate slightly for me just off idle. Low adj at 1 (with hi at 5/8), I could get it to lean stall. Turning the hi adjs out to 3/4 would help prevent the lean stall when going WOT off idle, but tended to produce more gargle at 1/4 to WOT. Low adjusters work best at 1-1/8 or 1-1/4, with the hi adjusters at 5/8...or maybe even 1/2...once we see how the wash develops. Or, may find that the low adjusters at 1 with the hi adjusters at 3/4 is preferred. Just needs to be ridden and monitored for a tankful or 2.


    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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