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Help FZR250 3LN3 carb problem.

Discussion in 'Yamaha 250cc In-Line 4's' started by Gert, Jun 15, 2016.

  1. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Mine definately had the 7 and 9 needles and theres no way they would have been changed/replaced from original



    The only ones listed on Ali are these .... Id have no doubt they arnt top quality either but buying full keyster kits is not a very good option

    https://www.aliexpress.com/item/FZR...12c4e7f&transAbTest=ae803_1&priceBeautifyAB=0
     
  2. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    I took the 5CT7 from the photocopied 3LN1 supplement in the resources section - yamaha-fzr250r-3ln1-service-manual-supplement.11

    What's the chances that your 3LN1 had 3LN3 or 3LN5 carbs or carb internals fitted?
     
  3. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    These are all 3LN1

    Ill send them all to forensics and report back :lolsign:


    IMGP1045 (Medium).jpeg
     
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  4. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    CSI Tamworth - who's got a gravelly voice? Can you take a shot to portray the world from the carburettors point of view? You're going to need some pretty coloured gels for the lights... :D
     
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  5. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    I pulled the bung on a spare body (sounds like an autopsy :cool: ) and it came off easily with long nose pliers but it is definately flakey on the edges and would pay to clean up the outside edge before re installing

    Its grungeville but I could see the light thru the openings but they could easily get blocked

    IMGP1053 (Medium).jpeg IMGP1051 (Medium).jpeg
     
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  6. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    I just checked the difference between the 5CT7 and 5CT9 against the Excel sheet that @maelstrom has http://www.litetek.co/docs/Mikuni_Needles.xls

    5CT7 5 53.5 2.6 18.00 37.50 50.90

    5CT9 5 53.5 2.6 17.50 37.00 50.90

    The 5CT9 begins it's taper 0.5mm earlier.
    So a 5CT9 with the e-clip 1 higher (leaner) plus a 0.5mm shim should be equivalent to a 5CT7 in the important ranges where it counts at the two taper positions - there is a diameter difference at the tip between these two, but basically at that throttle opening it should be all main jet
     
    Last edited: May 4, 2018
  7. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Yes, that is correct @ruckusman
    If anyone wants to perform medical experiments and fit new o-rings on the bungs,
    calculating for stretch and compression I make them to be JIS S8. You could get some
    at your local bearing shop. The o-rings in my carbs were in pieces and brittle.
     
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    Last edited: May 4, 2018
  8. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    @GreyImport OK thinking on this a little more perhaps your 3LN1 carbs were on the cusp of development of the 5CT9 needles.

    The 5CT9 in the centre carbs on the middle clip without the shim is equivalent to the 5CT7 with the clip in the middle position plus the 0.5mm spacer which is the original spec for the 3LN1.

    Nice to know the cross reference between those so we can gather 5CT9 needles and emulsion tubes on their own to be able to refurb
     
  9. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    I am waiting to see what happens if someone tries to run their bike with no o-rings.
     
  10. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    wouldnt that just mess up everything if fuel or air gets in via the bung?

    For those playing at home heres where the orifices inside the hole go to .... alot of potential for blockages

    bung hole 2.png
     
  11. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Yes, that is the point. To test what happens to a well running bike if you have leaky bungs. By the same token you could take a well running bike and fit some worn needles to see which one of those will cause chugging, problem solved, put it to bed. When the carbs are fitted, those bungs are at the bottom of the fuel chamber, so totally immersed, and there is a lower pressure on the other side of the bung. 1/4 turn on a pilot screw makes a big difference, so what then is fuel being sucked into that chamber going to do?
     
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    Last edited: May 6, 2018
  12. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Im with u now ... Thinking of FZR carbs always throws all normal thinking out the door ... and Ive been out pulling carbs to bits half the morning as well ... :D

    So I just pulled carbs from 1 and 2 cylinders down , which actually where the ones that came on @G1D1 s bike initially and we were told had been 'done' .... they are 3LN1s and the needles were both ct7s and the clips (no shims) were on position 2
    But Id guarantee these have been fiddled with ... not even the "right" carbs for the motor

    The tubes and needles actually look in good shape
     
  13. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    I just pulled another whole set of needles out .... all 5ct7s with shims , clip on 2

    Nothing yet is set to any base factory setting except these were close to your statement here




    @G1D1 ... if your going to play with carbs then get yourself a JIS driver ... best tool in the shed

    the #2 is the one I most use ... its a Vessel gel grip


    http://www.toolking.com.au/screwdriver-japanese-industrial-standard-motorbike-etc/

    https://www.2fiftycc.com/index.php?threads/dimples.1068/
     
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    Last edited: May 4, 2018
  14. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    @G1D1 - if you don't have a JIS driver posidrive will also work effecively, just be sure not to use phillips as they will ride up out of the screw very easily

    @GreyImport - that table is partially correct with the 5CT9 on the inners there doesn't need to be an extra shim below 2 & 3
    So it should read
    carbs 1 & 4 5CT7,
    carbs 2 & 3 5CT9
    all 4 with clip on 3rd notch no shim
    or
    carbs 1 & 4 5CT7 - clip on 3rd notch
    carbs 2 & 3 5CT7 clip on 3rd notch plus metal shim - equivalent to clip 3.5

    Both of those combinations are equivalent and this all now tallies perfectly with the Yamaha published 3LN1 supplement and other specs I have seen.

    I'll do a writeup later which will allow us to do the reverse conversion using only 5CT9 needles, which are available, for all four carbs - would be nice to be able to just replace needles if they are wearing quickly
     
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  15. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    All this needle talk has got me thinking now, i wonder if the Keyster needle's were in the correct box's too ?
    5CT7's in the 2x outer carb's (1 and 4), and 5CT9's in the 2x inner carb's, (2 and 3)
    I cant remember seeing any number's stamped on the needle's ?
    Damn you guy's !! lol


    Maybe they confused themselve's with the noozle might have meant needle ?

    Keyster kit x2 K-1203YKU (KY)
    Motorcycle Repair Kit


    Yamaha FZR250 3LN3, 3LN5 INNER Carbs Numbers 2 or 3
    Original Carburetor No.: 3LN-14902-10, 3LN-14903-10


    Included in this kit:

    Chamber Gaskets (2)
    Needle Valve
    Jet Needle
    "E" Clip
    Screw Air
    Spring Air
    Noozle
    Main Jet #100 **
    Should be 97.5 main jet's in carby's 2 and 3
    Main Jet #42.5
    Slow Jet #100
    Jet, Air Bleed #112.5
    "O" Ring (7)
    Washer
    Screw Throttle
    Spring Throttle
    Other (3)


    Keyster kit x2 K-1203YKS (KY)

    Motorcycle Repair Kit

    Yamaha FZR250 3LN3, 3LN5 Outer Carbs Numbers 1 or 4
    Original Carburetor No.: 3LN-14901-10, 3LN-14904-10


    Included in this kit:

    Chamber Gaskets (2)
    Needle Valve
    Jet Needle
    "E" Clip
    Screw Air
    Spring Air
    Noozle
    Main Jet #97.5
    ** Should be 100 main jet's in carby's 1 and 4
    Main Jet #42.5
    Slow Jet #100
    Jet, Air Bleed #112.5
    "O" Ring (7)
    Washer
    Screw Throttle
    Spring Throttle
    Other (3)
     
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  16. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    I've got 4 kits here for 3LN1 - not yet fitted, I will measure the needles and let you know if there is any difference between them.
    It should be easy enough to see where the tapers begin, which is the only difference between them essentially
     
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  17. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Not me, mine are Nickel plated, and look the same as when i fitted them last time i looked
     
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  18. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    OK so I've done a visual between inner and outer carb needles from the keyster kits for 3LN1 and they are identical - the lower taper which is easy to identify comes in at exactly the same point in relation to the notches - so fair to assume they are 5CT7 equivalent.

    So for correct fitting - the centre 2 carbs have the 0.5mm metal shim as per the 3LN1 supplement.
     
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  19. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Thats the configuration Ill run when I eventually redo my carbs ... and rebuild a set for the drag bike .... I have an abundance of used 7s that actually look 'not too bad'
     
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  20. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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