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  1. #1

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    [2001 XLT 1200] Beginner Mikuni BN44 Rebuild Questions

    First-timer attempting a carb rebuild. I will be starting tonight. I have some questions before I begin.

    Running progress album here: http://imgur.com/a/BZeC7

    Regarding Pop-Off:
    I have 3 MK-BN-RY12RB rebuild kits. They should come with 95-gram springs.
    The pg 15 of the manual @ http://www.mikuni.com/pdf/sbn_manual.pdf has a pop-off chart.

    To verify pop-off settings for my stock setup (accel pump and stock airbox) do I follow these steps?
    1. Verify what spring I have in the rebuild kit by color.
    2. See what size needle valve I have.
    3. Use the mikuni chart to determine correct pop-off.

    How do I determine my needle valve size?

    Will I find the needle valve size on the seat? The post below mentions size but I am not sure if he means needle valve size.

    Quote Originally Posted by mudslanger View Post
    If no one has changed them you can find the size on the seat if you pull it out..
    Next question: It appears that the stock mikunis may come with a 1.5-sized needle valve.

    For a stock setup, accel pump and stock airbox intact, should I be looking for a 43 psi pop-off as listed in the Mikuni chart (assuming 1.5 NS, 95 g spring), or should I be looking for a 62 psi pop-off as suggested in the post below?

    Quote Originally Posted by LT1GMC View Post
    The stock boats have a super high pop-off, and once they pop they will leak by after the pop, so you have to back the pressure clear off and start again to confirm your results. I cut 1 1/2 coils off each of the stock spring to get pop-off down to around 62 lbs. You also can "tune" the pop-off to equalize them by small adjustments to the arm.
    I am confused about the stock setup pop-off because of this post:

    Quote Originally Posted by OsideBill View Post
    110 Pilots
    125 Mains
    1.5 Needle and seat
    95 Gram Spring (dull silver)

    This will give you low to mid 40's pop off. You also want to disable or remove the accelerator pump. set the low speed screw at 1 turn out and high speed at 1-1/2 out. if you are running stock air cleaner run a 115 pilot jet.
    Bill is mentioning a mid-40's pop-off, similar to the Mikuni chart, be he's talking about a setup without the accel pump and I don't know how the 110 & 125 jets compare to what's in mine.

    I thank you for your help. All the time spent posting solutions is very much appreciated. I am looking to understand the principles behind these things, eventually.
    Last edited by D-Sect; 08-31-2012 at 11:35 PM. Reason: Added photo album link


  2. #2

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    It begins.

    Workspace.


    Corrosion inside? We'll find out.

  3. #3

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    Good luck, I haven't did mine yet, still waiting on some parts. Man that one carb sure looks rough.

  4. #4
    mudslanger's Avatar
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    The stock needle SEAT in those carbs should be a 1.2
    Try to get the popoff to around 45psi do not bend the little arm.....if they are bent replace them with the new ones in the kit.
    if you are running the stock air box and pretty much keeping it stock then don't mess with the highs and lows adjuster screws. you can even leave the accel. pump and stock jets and needle seat but pull it out and replace the O ring on the seat.

  5. #5

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    Comments in-line:

    Quote Originally Posted by mudslanger View Post
    The stock needle SEAT in those carbs should be a 1.2
    Can you ID the needle seat by listing its # from this diagram? > http://www.mikuni.com/pdf/sbn_rebuild-kit.pdf

    Try to get the popoff to around 45psi do not bend the little arm.....if they are bent replace them with the new ones in the kit.
    if you are running the stock air box and pretty much keeping it stock then don't mess with the highs and lows adjuster screws.
    Def. running stock air box and stock everything (except D-Plate). Don't I have to change the o-rings (#s 8 and 9 on the diagram)? I removed the tamper cap and hi-speed adjuster and spring on one carb. Didn't see the washer (#26) yet and didn't do the low-speed yet. Will do that stuff later, if needed.

    you can even leave the accel. pump and stock jets and needle seat but pull it out and replace the O ring on the seat.
    The O-ring on the seat is # 10 on the diagram?

    Thanks for the info!

  6. #6
    silvercrxsir's Avatar
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    Those have a 1.2 needle and seat and a 115 gram spring and popoff is between 70-80psi.if you drop the popoff to 45psi it will run real rich and you will need to rejet.these skis have real high popoff and are jetted lean for emissions which is why they have an accelerator pump.if your using the stock airbox and keeping the acc pump then don't change any settings.also note when you change those clear round plastic discs in the pump side,the side with the green marker on it will be facing you.the mikuni and yamaha manuals don't mention this at all

  7. #7

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    Here are some pics and tips that may help fill knowledge gaps for total newbies like myself who are using popular online resources as guides. I am using the Yahama service manual, Fernando's (http://www.hydrotoys.com/gpr/tuners/...orAssembly.pdf) and CajunDude's (http://www.cajundude.com/carbrejet.htm) illustrated guides.

    Recording the idle screw setting with a photo:


    Using air hammer to remove throttle link:

    (j/k - it was only the tip, I promise!)

    Tip: The throttle link is flexible plastic. The service manual simply says remove it. Removing it means prying it off the ball end as shown above. It will not crack as easy as it appears.


    Starting with #1, because it looks like trouble:


    Checking pop-off setting before starting:

    Inconclusive. Must test again.

    Tip: Use a shop-vac filter to cradle the carb instead of a vise for impact driving the screws out. This is nice because the rubber eats the downwards force and also because it was 2 feet from my workbench. Make sure you're supporting the casting.


    A little stuff in the thinger (technical terms):


    Looks nasty, but wound up being later removed with a nylon brush:


    Tip: Record multiple parts using a sheet of paper. I marks-a-lot and ziploc bag all parts in groups. I use paper & a photo as a callout:


    Most of the stuff from inside. I used impact driver on the 2 valve body screws:


    Pump side:


    Picks are handy:


    Oh. This looks bad. Good news is, when you take the pump apart you can totally see how it works.


    I have a lot of goodies to clean the crap off these. Chem Dip, Sand Blaster, Vibratory Tumbler, Ultrasonic Cleaner. I used baking soda in the sand blaster and it took off the glazed varnish. It also cleaned the gasket area perfectly, and made everything really smooth, without taking away metal. It's still stained though, but you can't feel it.


    I am fairly certain that all that crappy stuff will clean up nice, or is this a dead carb?

    Removing the tamper-hamper caps: Fernando used a slide-hammer in his guide, I used vise grips. I drilled about 1/8" deep into the cap with a 5/32" bit and then used a real fine bit to punch a hole through the cap and bottomed the drill bit into the screw (doh!). I used a self-tapping screw and screwed it into the cap.

    I locked the screw into vise grips and held the carb by the vise grips over some soft carpet and smacked the vise grips sideways with a hammer and let the carb fall:


    Use a positive stop on the drill bit to prevent from drilling too deep. Good example here: http://www.hydrotoys.com/gpr/tuners/...CapRemoval.pdf

    Summary so far:

    Carb filter was real clean. Everything came apart easy.

    The hi-speed adjuster screw that I hit with a drill bit - I don't know if it turned, but I doubt it, given no real mark on the screw head. It was 1/2 turn out, so that's the setting I recorded.

    You must use some kind of impact-action tool on some of the screws. You can get by with a Harbor Freight one (http://www.harborfreight.com/impact-...ase-37530.html - $7 DOLLA) if you don't have anything around.

    My questions are:

    Is this carb dead? Is that fatal corrosion, or just salt stuff (I'm all saltwater)? How do I know if a carb is a goner? If it is, oh well.. Good training wheels. The Mikuni manual is a great read and I recommend it to any beginner.

    More updates as they come..

  8. #8
    silvercrxsir's Avatar
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    It doesn't look bad at all usually the main reason that would cause them to be considered junk is if the adjusters or jets get seized ,just clean them up real good,I like to paint them with vht epoxy paint in a spray can since most other paints won't stick to alum and you won't need and can't use an etching primer with epoxy ,I usually spray them down good with distilled white vinegar in a squirt bottle and let them sit for 5 min then rinse them off with water and air dry or use compressed air.this will "etch" the alum so paint will stick.

  9. #9

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    My plan was to soda blast / ultrasonic the insides, glass bead the outside, then paint. Epoxy paint sounds great.

  10. #10
    mudslanger's Avatar
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    If you want your boat to run good and have a crisp throttle response set your pop off pressure to 45 psi no less and not over 50 psi.

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