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Help FZR250 3LN3 carb problem.

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

  1. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    If the float height is 16mm, therefore fuel level is 9.2mm, then they are correct and the problem lies elsewhere.
     
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  2. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Perhaps good to check all settings:

    fuel height?
    pilot air jet out how many turns?
    bogging low revs, perhaps a little to rich (pilot air jet) and idle speed a tiny bit too low

    over 12K running rough I'm with Grey - look at the EXUP valve initial setting and free motion when operating

    I had my EXUP cable break and the 3km ride home was difficult, no power down low and no revs
     
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  3. Joker

    Joker See "about me" for contact details. Contributing Member

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    What is your mixture screw/pilot screw setting? Mine are set at 2.75 turns out but my needles/tubes are a bit worn. Is your needle setting also at stock (ie in the middle notch)? If they are new I'd start with the middle notch and 3 turns out, adjusting in 1/4 turns from there.
     
  4. Gert

    Gert Well-Known Member

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    Jets are good, mixture is 3 turns. Exup ok.

    Since the bike was running normal before the tube problems, I decided to bent the float tabs back to where they come from.
    Yesterday, it was too late to test again, maybe this evening.

    Made an cardbord tool to measure this 16 mm float height (not easy to measure) and set all four equal.

    Let you know what happens.
     
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  5. Joker

    Joker See "about me" for contact details. Contributing Member

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    Just make sure you're not changing too much at once or you'll be forever tinkering, but good luck.

    If you post up a video of it running we'll all be able to offer some thoughts a bit more accurately.
     
  6. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Heres mine with a pinched diaphragm on #1 ..... which of course gives u a dead slide

    Also check that this o ring is present and correct

    cap o rings.jpg



     
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  7. Gert

    Gert Well-Known Member

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    Busy lately and spent some time riding the other bike:
    http://2fiftycc.com/index.php?threads/hello-from-holland.8769/#post-90907

    So, during time, I got an idea. Since I tuned my car engine (and others) and installed an EMS, I am in the happy possession of an wide band Air/Fuel device.
    Since this device is collecting dust at the moment, I digged it out and installed it in the exhaust.
    First I made an test with the CBR250, so I have an reference, than I looked at the FZR.

    Now I could see, A/F was way to lean. So I adjusted the fuel levels again and now I do have an nice and steady idle and blipping the throttle is agressive again, like it should be.

    I took a pic and on the right you can see the CBR with removed silencer, otherwise the sensor would not fit.

    [​IMG]

    This evening I am trying an testrun outside again, and let's find out what happends.
     
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  8. Gert

    Gert Well-Known Member

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    Went for a drive yesterday and the bike is almost fine. Drove about 120 kms.
    Only time she hesitates is when I am engine breaking from 18.000 rpm and at 16.000 rpm I give WOT, there is a little hiccup.
    So I am adjusting the fuel level a tiny bit and then I hope this operation is finished.
     
  9. Gert

    Gert Well-Known Member

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    Allright. Did bite the bullet and made an testrun with the wideband connected.
    First I took a spin with the CBR250 and looked closely at the A/F ratio.
    It appears to be pretty lean, but I am already driving for years with it now.
    Then I made a drive with the FZR and she was nice and richer than the CBR.
    So, I decide to leave it there. She runs fine and strong, with no hesitations.

    If I find the time, I will see if I can richen up the CBR a little. Idle is lean and throttle too. Maybe a bit more fuel via the mixture screw and the needles a notch higher.

    At last a pic in test config:

    [​IMG]

    Many thanks for all the help.
     
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  10. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    that bike is beautifully clean - I hang my head in shame
     
  11. Khasitsophat

    Khasitsophat Member

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    i got a problem with my FZR250R 3LN3 . How to fix when I start always rpm 10000 can not adjust air. (Already change engine oil, oil filter) and another problem is when I'm try full throttle rpm gones down.
     
  12. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    I would suggest checking all of the slides, springs, diaphragms and the top cap o-rings. also the choke plunger mechanism and parts. The throttle cable and return mechanism would also need to be checked.

    If you want to sell your 250 in the future, please contact Da at 098-928-9860 (Khon Kaen).
    cheers
    Blair
     
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  13. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Also check the intake manifold's aren't split, and that the carby to airbox rubber's are in good condition
    To check the intake manifold's are not split, starft the engine and let it run, then spray some wd40 or similar on the rubber manifold's below the carby's.
    If while doing this the engine rev's change in any way then there is a vacuum leak, most likely from the intake manifold's
     
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  14. Gert

    Gert Well-Known Member

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    Since the new stuff in the carbs and setting the fuel levels good, the bike is much more efficient with fuel.
    Before, we got about 180 kms before the fuel must go on reserve, but now it is about 220 kms.
    That looks better, since the CBR250 was always much better on fuel, but now they are the same.
     
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  15. G1D1

    G1D1 Active Member

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    Hey @ruckusman, did you ever sort this problem?

    I am having the exact same thing. I've checked fuel filter, petcock, checked for spark and plugs (all fine), and now thinking I need to have a dig at the carbs but want to make sure I have all the parts I need before taking apart.

    Any advice would be much appreciated :)

    Thanks!
     
  16. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    As always, it is likely the needles and emulsion tubes being very worn, and excess fuel is flooding the cylinders.

    You can test this when it happens - shut off the fuel and keep the bike alive until the available fuel starts to drop, the bike should come alive again.
     
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  17. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Get some Keyster kit's and fit them, set the float height's to 14.7mm if you have the 3LN3 carby's on it still, this will give you a fuel level of 10.5mm above the line with the ign / fuel pump on, then warm the bike up and tune it to suit.
    I played around with my 3LN3 for a long time and finally got it all running sweet.
    Mine also had hairline crack's in the inlet manifold's so that didn't help either, but you can get them cheap now off ebay (around $32 for the set of 4 inc delivery)
     
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  18. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    @G1D1 - what @Linkin said is absolutely spot on

    motorcyclespares warehouse has the keyster kits

    https://www.motorcyclespareswarehouse.com.au/products/k-1203yku-ky-carb-repair-and-parts-kit

    https://www.motorcyclespareswarehouse.com.au/products/k-1203yks-ky-carb-repair-and-parts-kit

    Please be aware that just reading the description of each of those kits they have made a mistake on the main jet numbers which are packed and written on the packaging. It lists - incorrectly #97.5 for carbs 1 & 4 and #100 for carbs 2 & 3.

    @my67xr first correctly identified the error with the keyster packaging/labelling and @Joker bumped into the the consequences of this problem very recently when his bike with freshly rebuilt carbs wouldn't rev past 10K because of the wrong inner and out carb main jets.

    This can be confusing so...
    To be clear for anyone else just reading this post on the FZR's the outer cylinders run cooler all the way through the inlet tracts -> cylinder head and cooler denser air requires more fuel thus larger main jets.
    Similarly the inner cylinders run hotter through the inlet tracts -> cylinder head and hotter less dense air requires less fuel thus smaller main jets.
     
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  19. G1D1

    G1D1 Active Member

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    Great, @ruckusman so just to confirm, I need put to put the jets as follows:

    Carbs 1 & 4: #100
    Carbs 2 & 3: #97.5

    Will let you know how I go. Do you know of any good step by step guides for taking apart these carbs by the way? I’m sure there is plenty of knowledge on this forum, but never has done it before so would be handy to have close by!

    Thanks so much!
     
  20. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    @G1D1 - whereabouts in Sydney are you?
    I'm in Narrabeen and about to pull my 3LN1 carbs down once I've removed the engine from the frame - though it won't be my first time pulling the damn, whoops I really meant truly lovely and adorable, carburettors apart...
     
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