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Project My FZR250 3LN6

Discussion in 'Your 250cc Projects' started by driftwood, May 10, 2020.

  1. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Ah, thanks mate :) I will add a note to my guide page about fuel levels.
     
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  2. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    That chart was made a while ago by @beano
     
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  3. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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  4. driftwood

    driftwood Member

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    I'm sure the petrol sniffing is getting to me. Mucked about for ages - nothing made sense.
    Used manometer to test fuel height - it was ridiculously low, even with an elec pump ensuring supply. Of course I should get fresh springs/needle for this procedure, but reckon probs lay elsewhere. Bowls had ~60ml ea, pushed float tab and now ~45ml.
    Noticed jet needle tip sitting at diff heights. Arrgh... there's a locating divot on the needle seal that wasn't in its hole (part of assy 34 in parts diag). Broke them off.
     
  5. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Sounds like you should have stepped back to make an assessment.

    First step would have been to actually measure the fuel level to get your starting point, it's just done with a piece of clear hose, the photo in the post I linked to above has a 1ml syringe with plunger removed to sight the fuel level

    Here's an easily accessible parts fiches for the zeal, similar carbs, which part is now broken off?

    http://www.firstclassmotorcycles.com.au/partFinder/fiche/yamaha/1998/fzx25-zeal/carburetor#content
     
  6. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Sound's like the plastic spacer under the needle clip, part of #34 in the diagram below
    If you look closely you can see the little locator pin
    The Keyster spacer's don't have the little plastic pin on their replacement spacer's so it shouldn't be an issue

    [​IMG]

    [​IMG]
     
  7. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    What was your full process to o/haul the carby's ?
    And what did you use to clean them ?
    Did you fit new jet's and seal's ?
    And have you checked the fuel level's yet? They should be 10.5mm above the line on the middle outside's of the fuel bowl
    Or the float height's need to be set at 14.7mm from the fuel bowl mounting face

    65ml's of fuel in each bowl doesn't sound much, but then again i have never measured how much they hold


    @GreyImport @driftwood need's his own thread for this 3LN6 instead of being added onto to neoncrypnid's 2KR thread
    EDIT: done
     
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    Last edited: Sep 6, 2020
  8. beano

    beano Well-Known Member Premium Member

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    Thanks @my67xr.

    Yes, I made that chart a few years ago while I was trying to compile a definitive source of info for the FZR carbs. At the time there was various conflicting information floating around and seemingly no coherent information for getting them dialed in properly.

    Having a base setting to work from is an important first step in diagnosing running issues and at the time I did a lot of searching of Japanese websites using google translate to try get the full picture, which led me to blogs such as this where the chart idea was born:

    https://c-ueda.at.webry.info/200901/article_7.html

    The 3ln-1 and 3ln-3/5 info is correct, as I own a couple sets of both carb types and could confirm the information from the parts lists and service manuals etc. This also includes the clarification (which I believe is correct) from ruckusman regarding the interchangeability (with shim) of the 5ct7 and 5ct9 needles, both of which are listed in the Yamaha parts book and service manual.

    However, the 3ln-6/7 and zeal info is only as accurate as what I could find online at the time, (there was no service manual available to download for these models, I don’t know if that has changed in the years since) So they need to be taken as a guideline only. I’m happy to update the chart if anyone can provide the correct info (preferably info that can be verified from the correct parts books and service manuals).
     
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  9. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Thanks @beano for your service :)
    Hopefully someone will buy the Zeal & 6/7 manual supplements in the future and all will be revealed.
     
  10. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    There is this site, spec sheet for all of the tightening torques I believe originated from there

    https://sites.google.com/site/yamahafzx250zeal/home

    Good information on this page
    https://sites.google.com/site/yamahafzx250zeal/Manuals
    This specifications PDF is already in the resources section
    https://www.2fiftycc.com/index.php?resources/yamaha-fzx250-zeal-specifications.128/

    It does give the fuel level as 10.5mm and all of the other carb specs look to be correct, for instance the needle type is correct for the zeal
     
  11. driftwood

    driftwood Member

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    I'm making no progress in trying to get fuel levels 9 or 10mm above the line - in fact I'm losing cylinders as I work (but plugs aint wet, sometimes thinking the petrol sniffing is unhelpful). But can confirm the guess at this page of 'above', by pattern matching the katakana char 高
     
  12. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    On your carbs it's the casting level which is highlighted by the red arrow on the carbs pictured on that page you've linked to, and it's above that line
     
    Last edited: Sep 10, 2020
  13. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Have you set the float height's to 14.7mm when the tab is only just touching the pin on the inlet needle ?
     
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  14. driftwood

    driftwood Member

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    I didn't change the needles, so this setting doesn't work on the weak, old springs. The manometer check of fuel level shows all BELOW the cast line, yet I've bent the tangs substantially away from the needle.
    I'm sure my problem is spark. I clean the plugs more thoroughly between runs (using ohmeter to check for carbon, and verifying spark before re-installing). Smoke is getting much less with every day (as someone commented re valve stem seal hardening on a bike that aint been run in ages). Avg compression across cyls is 147psi, so loathe to strip down... when I'm not allowed to actually get it going and have a run!!! Wasting time until lockdown eases ;)
     
  15. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    The 14.7mm measurement is still needed to be set right even if the spring for the needle pin is weak

    I just pulled out an old 'part's' carby which also has a very weak needle pin spring in it
    The float tab is set so the float height is 14.7mm off the fuel bowl mounting face when it just touches the pin, the spring doesn't really come into it, it shouldn't be compressed at all
    The float tab should be bent toward's the needle not away from it
    You can see in my second and third picture that the tab is bent slightly down from the float toward's the needle

    Having your float tab bent up / away from the needle will give the carby a super low fuel level and will struggle to run

    20200911_164803.jpg 20200911_164905.jpg 20200911_164913.jpg
     
  16. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    I have found the best / easiest way to bend the float tab is with a sewing needle put into the hole in the float tab and push it down.
    Bending this tab any other way can cause the tab to twist and make's it hard to get a consistant float height

    [​IMG]
     
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  17. driftwood

    driftwood Member

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    Float height is only a surrogate for fuel level - and that's easily checked against the service data. My problem has been that as I lift the tang and get fuel level up past the lower casting line, I've found the oil level rising.... aaarghhhh. It's flooded.
     
  18. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Yes it is, but try setting the fuel level without knowing what the float height is.
    I spent a long time working it out on my 3LN3, before i bought the 3LN3/3LN5 supplementary service manual

    For the leaking needle's you'll need 4x of these then
    https://www.motorcyclespareswarehouse.com.au/collections/keyster-aa-needle/3gm-14107-17-00

    The jet housing seal's are known to leak when they shrink, the mixture screw seal's shrink and leak air, and you should replace the float needle housing seal's while you are at it too

    But then again if you haven't replaced all the seal's you may as well get a Litetek seal kit and fit them
    https://litetek.co/Carb_Kit_Yamaha_FZR250_3LN6.html
     
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    Last edited: Sep 11, 2020
  19. driftwood

    driftwood Member

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    My bad. Cyl with inlet manifold puddle was set too high. Think order of restoration should be 1. New specs; 2. Mindfulness course to get the Zen; 3. Clean out tank better; then 4. Work way down the bike from the top ... (rather than just shortcut so as to get it out for a ride).
     
  20. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Sounds like you definitely need new seat needles - first thing
    That oil has to go as it's been contaminated with fuel
    Then get across setting that float height - the carbs aren't sitting on their tops when doing float height, you can prop them on the correct angle any way that you can manage, because you've been adjusting the tang, there will be some work getting them set correctly - that sewing needle tech is GOLD

    I did the equivalent of the @my67xr piece of plastic with the cutout with a playing card

    FWIW - the softness or hardness of the needle seat spring doesn't make a significant impact on float height because with the spring uncompressed and the float tang just touching, there is no compression of the spring whatsoever and the needles will be the same length - then check the fuel height with the carbs on the bike

    Then if if it's out you will need to adjust the float height
    The formula is fuel height plus float height equals 25.2mm
    So as one increases the other decreases because the two measurements should always sum to 25.2mm

    Sounds like you've been adjusting the float height higher if the fuel height is getting lower
     
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