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Pinned Needles and needle jets/emulsion tubes - FZR250 Mikuni BDST28 Carurettors

Discussion in 'Yamaha 250cc In-Line 4's' started by GreyImport, Sep 17, 2016.

  1. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    From http://www.factorypro.com/Prod_Pages/prody85.html
    Info about the" "Slide Step / Notch / Ledge"
    The 1/3 width step, built into the slide, where the needle sits, is designed to lessen the "rattling" that the needle does in the needle jet (you, know.... the hole that eventually wears out in every carburetor with a slide and causes the bike to run rich over time). It tries to keep the needle leaning up against one side of the hole , instead of letting it rattle and beat both sides of the orifice oval..... That step is in most Yamaha Mikuni carbs for the last decade or two - The needle jet still wears, but at a slightly slower rate.
     
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  2. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    By the way, the needles advertised on the Chinese website
    " 5CT9 total length is 54mm, the thickest section 2.5mm, the end 1.1mm"
    and according to the spreadsheet I have
    5CT9 total length is 53.5mm, the thick end is 2.515mm, the end 1.046mm

    Of course this may not be correct. The spreadsheet does not have Mikuni Corporation written on it. I wonder where the Chinese get this stuff? Maybe they bribe somebody from a factory to copy some drawings for them.
     
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    Last edited: Oct 3, 2016
  3. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Smart boy :lolsign:

    IMGP0902 (Small).JPG

    The needles in the slide are really loose ..... and yes the red circled wear would be from movement in the slide housing at Id assume, all the rev range and the blue circled wear would be from the low rev range ..... as positioned in the pic below (worn area sitting at the entrance to the tube) .... and from my vid the other day thats where the slide gets to when just blipping the throttle.

    So do we have worn slides to add to the mix ? :cool:

    IMGP0903 (Small).JPG

    IMGP0906 (Small) arrow.jpg
     
  4. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Where did those 638 series needle jets originate?

    Still nothing available in either the 625 or 638 series anywhere to be found...
     
  5. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Why thank you ;)

    I've been thinking that is a very good possibility
     
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  6. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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  7. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Given the effort that Mikuni went to, to hold the needle down.
    [​IMG]
    I think perhaps a lot of the problem is the vacuum trying to lift the damn thing up. More than trying to keep it dead centre.
    If you consider all that wear on Mr Greys' needle is where it is held in the slide, and that there should only be 0.037mm clearance when new then it could be not just caused by to and fro movement but also by up and down.

    I cannot see that it will be possible fix the needle exactly so that is on the same axis as the emulsion tube. Maybe it is possible but more likely the needle will off centre and it will rub against the emulsion tube and wear out.
     
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  8. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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  9. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    .... and I just realised what the differences are :prankster:


    Tube holes (Small).png
     
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  10. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    They're the same with the 3LN3 and 3LN5, 2x different needle's inner and outer's, then 3LN5 and 3LN6 have 2 different needle's again inner and outer's.
    Then the Needle jet's are the same 3LN1, 3LN3 and 3LN5, and they use different Needle Jet's on the 3LN 6 and 3LN7

    Yeah worn slide's certainly wouldn't help needle/needle jet wear.

    3LN Needle's


    3LN1 use's 3LN 1490J 10 and 3LN 1490J 00, with 3LN 14141 28 Needle Jet's

    3LN3 and 3LN5 use 3LN 1490J 20 and 3LN 1490J 30, with 3LN 14141 28 Needle Jet's

    3LN6 and 3LN7 use's 3LN 1490J 50 and 3LN 1490J 40, with 3LN 14141 37 Needle Jet's
     
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  11. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Here is the Honda solution
    [​IMG]
    I think stopping the vacuum might be important.
     
  12. Grasshopper

    Grasshopper Well-Known Member Dirty Wheel Club

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    Time to change to Hondas??? :cool:
     
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  13. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    which Honda does that come from?

    edit just read - MC22 above
     
  14. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Can we retrofit that part somehow, I like the look of the o-ring holding that securely in the slide so that it may move but not wobble freely
     
  15. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    From the parts book it looks like it has springs on both sides. Have to find a Honda MC22 owner. Anyone know where they might be?
     
  16. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    ..... Eastern Creek :crazypilot:
     
  17. Gidanski

    Gidanski Member

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    I have a CB400SF, same carbs as MC22. There is a small spring on the inside of the retainer, It clips into place at the bottom of the slide above the needle when you reinstall it, make a posotive lock that needs some force to be removed and luckily enough there is a thread on the outside and is the same thread as the top cover screws for easy removal, and the slide spring just sits around it to hold it all down.
     
  18. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Kiffsta has sent me some MC22 parts and when they arrive I will see if I can design something for the Yamahas.

    If you have some pictures @Gidanski that would help.
     
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  19. Gidanski

    Gidanski Member

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    Had to fiddle with the shims under the needles on it anyway. As you can see down there is a slight groove machined into the slide for the O-Ring to locate into.
    [​IMG] [​IMG] [​IMG] [​IMG]
     
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  20. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    I can't determine the scale of the two components from any photos...
    How tight or loose is the shim on the top section of the needle inside the bottom of the retainer?
     

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