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Help FZR250 3LN3 carb problem.

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

  1. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Those illustrations are very good - for reference the 3LN series needles are 2.515mm diameter - the emulsion tube hole diameters (n-8) are 2.590mm so that 0.075mm - yep you read that right seventy five thousandths of a millimetre clearance past the widest part of the needle.

    It doesn't take much wear to affect the amount of motion lotion coming up that tube at idle and screwing things up...
     
  2. Grasshopper

    Grasshopper Well-Known Member Premium Member Dirty Wheel Club

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    From memory, the emulsion tubes were done and solved the chugging problem at that time..but I don't think a Litetek kit was done on those carbs..
     
  3. G1D1

    G1D1 Member

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  4. Joker

    Joker If you want me find Club250 on facebook. Premium Member Contributing Member

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    I have a lot of parts left over from 4 sets of keyster kits if you're interested. Includes jets, needles, emulsion, float valves etc. All brand new. Only really missing some of the seals and a few bits and pieces like needle clips. PM me, will move them on cheaply (they're $50 PER CARB otherwise, what a rip!)
     
  5. G1D1

    G1D1 Member

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    Hey!!

    If anyone still interested (@maelstrom ) I’ve changed the pilot merge chamber o-rings and no success.

    Good news is now the problem is happening constantly, rather than intermittently. (Throttle very unresponsive and boggin down in low revs, struggles to build revs). Thought it could have been diaphragms but they are all good.

    Will rebuild carbs tomorrow with new jets and emulsion tubes and see if that fixes it!
     
  6. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Okay @G1D1 agree with you there, better to have a constant fault than an intermittent one. Is there much wear on your needles? Apart from the emulsion tubes, jets don't wear out they only get blocked. Look forward to your next post.
     
  7. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Did u clean and blow out the orifices in the merge chambers? .... 1 goes to the pilot jet and another to the pilot screw and the group of tiny holes in the centre go to the throat at the butterfly
     
  8. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Emulsion tubes should suffice and probably a good first test so you can narrow down the cause to a single element.

    Which jets do you have replacements for BTW?
     
  9. G1D1

    G1D1 Member

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    I have bought rebuild kits, so will be able to do everything I think. @GreyImport i cleaned and blew out with compressed air.

    Could it be blocked jets causing this?

    Needles I wasn’t sure what to look for, they look fine only a few marks on them. (Pictures attached!) Will check emulsion tubes for wear after replacing.

    3CEBB89C-8D26-487F-9E13-2FADC7198704.jpeg BA8EC343-A43F-4CE7-A10E-EA9D3033411F.jpeg F482624E-AD86-4388-B48E-1AD284616985.jpeg
     
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  10. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Those needles look like they have the normal marks on them .... its the inside of the tube that usually shows actual wear

    look for a groove where the needle has worn a path ... check out the file Ive attached

    Take out all the normal jets and look for blockages and use compressed air on them too .... not a piece of wire or wateva ..... be very careful with the pilot jet as its very soft brass ... make sure the screwdriver u use is a good fit on the head

    jets.png

    Make sure this o ring is in place when u reassemble

    oring.png
     

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    Last edited: Jun 3, 2018
  11. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    What are your mixture screw's set to, mine run's best with them at 1.75 turn's out.
    But then again i have the Keyster kit's put through them.
     
  12. G1D1

    G1D1 Member

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    Mine were all different! See attached...

    Does anyone know where the jet air bleed is? Can’t find it, but my kit has a new one.
     

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  13. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    On the air filter side of the carby
     
  14. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    5 turns out on mixture screw???????
    Your needles show virtually no wear at all. I would set the float heights and adjust the mixture screws before fitting all these new parts.
     
  15. Andych

    Andych Senior Member Premium Member

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    Wow.. 5 turns out.. Do as @maelstrom suggested.. and listen to what @my67xr has to say.... he has documented sorting these carbs out in infinite detail. You will need patience :)
     
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  16. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    If you put a razor blade against those needles and held it up to the light I wonder if there is wear there to be seen.

    It's ambiguous from the pictures if there's a little bit of soot on the needles making them look worn, or they are in fact worn, or perhaps both.

    This has me wondering if there is wear there, then perhaps it's symptomatic of the hole through the slide being worn and accelerating the wear on the replacement needles and emulsion tubes
     
  17. G1D1

    G1D1 Member

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    No luck with the rebuild kits, bike still isn't starting. Set fuel mixture screws to 1.75 turns out.

    Will try some more tinkering through the week, perhaps check fuel pump. I have put new plugs in yesterday, any other suggestions?
     
  18. Andych

    Andych Senior Member Premium Member

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    Float heights correct???
     
  19. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Excuse my lethargy at not re-reading the whole thread. it's a quick solution to read the fuel height with the carbs on the bike
    check
    https://2fiftycc.com/index.php?threads/my-fizzer.872/page-32#post-15537

    Now some thing I didn't think of originally was clear fuel resistant silicone tubing should be available at a mower shop for simplicity - there is no real need for the syringe two pen lines will suffice

    That will rule in or rule out fuel supply.

    Now don't know if you mentioned it not starting previously, that could be spark related, I notice you replaced plugs, someone else will have to chime in here if problematic clutch and/or side stand and/or neutral gear switches can cut the spark. It's just been too long for me and mine isn't running ATM to be able to check
     
  20. G1D1

    G1D1 Member

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    Checked fuel heights, all good.

    Found one pin on the coils slightly loose, tightened up and went to start, still not starting.

    Bike started with a little fuel dropped into each cylinder, and no more lazy throttle (previous problem). This leads me to think problem was intermittent as coil drops in and out, leading to bike running on 2 cylinders.

    However, bike not starting, have checked spark and air flow, tested fuel pump, set float heights and bench tested bowls filling up. Any suggestions what to try next??? Thinking ignition timing? Any guides on how to test this??

    Thanks all!
     

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