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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. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Nah mine are all good, same with the tubes they still like new.
    I just bought some Keyster rebuild kits for my 3LN3 though so if i can make them last a lot longer then that'll save me some $$ in the long run.
    I have a set of BDS26's off a 2KR too as spare's, not sure what those needle's and emulsion tube's look like though.
     
  2. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    I was looking at the Keyster kit's this morning and noticed what might be a problem
    The plastic needle clip shim's are slightly oversize to the needle, this would allow the needle to move enough to cause wear on both the needle and the needle jet's.
    The hole through the middle of the top plastic seat for the slide spring is also oversize, same thing again it'll allow the needle to sit at an angle
    If these were made to be a slight press fit then that would make the needle's sit straight and there'd be less chance of the wearing
    I will look at the original plastic shim and seat and if they are a tighter fit i'll use them
    If not i'll make some new one's myself
    I wonder the clip shim could be made with a slightly larger o/d as well, that may help to stop it being pulled to one side?


    The plastic spring seat's could be redesigned and remade too, if they were slightly deeper to sit up in the spring a bit more, and the bore opened up and have a small flange at the top to accommodate a small spring similar to the Zeal carb's that might be another way of helping the needle's sit straighter too

    [​IMG]

    [​IMG]
     
    Last edited: Oct 2, 2016
  3. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    that slop in the shims is also present in the OEM parts, it's also there in the slide housing just to compound the problem.

    I did notice that with the 3ln6/7/Zeal carbs that I have, the larger spring retainer doesn't sit flush on top of the needle with the small spring retainer sitting on top of the needle which would be another source of potential movement.

    My solution will hopefully solve those issues at both and of the needle retention system - and it's going to be simple
     
  4. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Hello,
    From the other thread.
    No, none of those lathes are going to do it. Not without spending a bunch of money on them. Once you go down to ten microns or less things get quite expensive. For this job I am just going to use a very small manual unit that is made for such work and then spend the same amount on collets, headstocks, pin gauges etc.

    Mr Grey sent me some Fizzer emulsion tubes and when they get here I will cut them open and see if my plan is going to work.

    @ruckusman For your locking the needle in position design, it would be best if you can make it adjustable so the needle can be precisely aligned.
     
  5. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Can I interpret this as you think that the existing holes in the slides for the needles may or may not be properly centred?

    I'd like to know what you're thinking is on that

    I was planning on just doing the lower t-shape sleeve first and checking for wear, then add extra support to the upper portion of the needle if required
     
  6. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    It is not that I think the holes are not centred, rather that the needles are not a tight fit into the slide and are able to move too much. With the needle sitting in position, how far can you move the tip of the needle fore-aft? This is for obvious reasons of course, otherwise the needle, if wrongly aligned and not allowed to float, would scrape for its full length. It may be that the mounting method used on the 3LN6-7 models dampens rather than eliminates the movement of the needles and that this approach is used because the needles at idle may be vibrating in their mounts. Watching Mr Greys slides at idle one does get that impression. Only the Fizzer Factory Folks can give us some feedback on that/

    Looking at the spreadsheet - the N-8 emulsion tube is 2.590 and a 5CT9 is 2.515 at its widest point, so 0.075mm is the difference or 0.0375 clearance each side of the needle. This is where all the wear is occurring, at idle, and of course exacerbated by gravity as Mr Grey mentioned before. To my way of thinking the opportunity for greatest improvement to wear comes from changing materials. Metal on metal with fuel as the lubricant is always going to be horrible. I am quite confident that the material I am thinking of will result in almost zero wear.
    cheers
     
  7. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    That's where the tight fitting shoulder washer/sleeve washer comes in. A tight fit onto the needle and a tight fit into the slide.

    The slide plastic will have some give, though I think it should be quickly evident if the needle is scraping on the jet with a micro nickel coating on the needle - simple visual inspection
     
  8. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Heres some photos of some needles back when I was originally rebuilding the carbs and of the tubes after I pulled them out the other day ... to show the wear

    Worn needles.jpg
    Emulsion Tubes.png
     
  9. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Those first two needles and the second emulsion tube look really bad.
     
  10. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    WOW those needles are KAPUT - I had no visible discernible wear on mine from memory
     
  11. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Yea I picked out the best from 2 sets of carbs when rebuilding .... I think those needles were the worst ones but those tubes were what Ive been running so must have been the pick of the bunch at the time ..... but of course at that time we all hadnt discovered the scourge of worn needles/jets

    If u look closely at the 2 outside tubes , they arnt close to being round internally
     
  12. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    So looking at the more obvious wear points on the needles , and guessing off hand on how the carb works , what point of the rev range would cause this.... or am I heading up the wrong path?

    red = idle
    blue = ΒΌ throttle ?

    Worn needles c.jpg
     
  13. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    yes
     
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  14. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Id say the red are inside the bottom of the slide.
    The bottom of the slide is 8mm deep.
     
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  15. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    I did not measure them and @my67xr did, so he is most likely to be correct. They must be rattling around pretty badly to generate that much wear in the slide mounting area. Ruckus' sleeve idea has a lot of merit in that case even just to reduce that issue.
     
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  16. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    I can imagine that perhaps once upon a time those damned needles likely fit snug into the slides if that is the wear from metal on plastic - astonishing
     
  17. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    I thought the slides were coated aluminium.
     
  18. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Original needles are thicker ..... top of the pic are original needles and spacers ... very tight fit .... bottom ones are original needles with wat Im pretty sure are Keyster spacers that get super tight at the positions shown in the pic.

    As Ive mentioned before I put the old spacers on the Keyster needles and they were loose ... not a good thing I would think, as u have said

    IMGP0897 (Small).JPG
     
  19. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    I've got apart right now, definitely a high density plastic
     
  20. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    OK I just checked the Zeal carbs - Emulsion tube series number is 625 - which looks exactly like 529 upsidedown, the giveaway is the jet number is O-4, and the 4 can't be read upside down whereas N-8 can
     
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