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Help Nightmare FZR carbs/fuel system

Discussion in 'Yamaha 250cc In-Line 4's' started by logan anderson, Nov 3, 2017.

  1. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Will it rev out clean in lower gears?
    For all of the trials and tribulations that I endured with mine, they were all problems at low revs, higher RPM performance was workable, so if your fuel levels and other carb settings & components are good, the issue may be elsewhere

    But that said, never assume something is correct, that has caught many of us over time
     
  2. logan anderson

    logan anderson Active Member

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    yeah, lower gears and to 100 is fine, however above that I start getting.... more bumps like if you don't have the air box closed properly on other bikes.
     
  3. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Mine didn't like going over about 5000 or 6000 rpm's with the float's set too high.
    With the float's too low it had a hesitation down low at around 3000 rpm's.
    Have you tried running the mixture screw's a touch leaner?
    I have the Keyster kit's in my carby's and have found they run really well at 2 turn's out instead of the factory 3 turn's out.
    When tuning it (at operating temp after a ride) i have set it to be a touch leaner than recommended, the idle had just started to drop down from it's highest/smoothest point
    If you're Keyster kit's are similar i would be trying them mixture screw's at around 1.75 turn's out or maybe a touch more.


    With your bike not going over 100km's, have you tried a touch of choke to see if it improve's ?
    You could also try blocking off 1/3 of the air filter element with some 100mph tape and see if that help's too.
    That way you'll know if it's running rich or lean so can adjust the carby's to suit either via the mixture screw's or the float height's
     
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  4. logan anderson

    logan anderson Active Member

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    I took her out at 1.75 turns from the standard 2 which really didn't make much of a difference.
    If thats the case with your kit maybe I should test 1.5 and see what happens then....

    a gas analyzer would be ideal at this point
     
  5. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Can't remember sorry, but have you synced the carby's yet ?
     
  6. Joker

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

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    Is it hesitating to go further, like it wants to and can't or is it bumpy as though it is being pushed back. Bit hard to describe but there's a difference. The first is a lean problem the second is a rich problem.

    Based on your pilot settings at 2 turns I'd guess you're running too lean. I'd move to 2.5 turns to be honest, re adjust the idle and try again.

    My bike has always been stock or 1 up on the needles and anywhere from 2 1/2 to 2 3/4 turns out depending. Usually happy somewhere between 2.5 and 3 turns. Not saying it will necessarily be the same with your bike, but it depends a bit how you adjust everything. Also remember there are different main jets between carbies.
     
  7. logan anderson

    logan anderson Active Member

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    Main issue there is anything over 2.12-2.25 turns makes the idle setting defunt.
    I'm going to try adjusting the jet needle and see where that takes me

    I thought the 3ln1 was supost to be 2 turns and the 3ln3+ was supost to be 3 turns?
     
  8. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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  9. logan anderson

    logan anderson Active Member

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    I'm going to say it's more between a being pushed back / dosent want to go further
     
  10. Joker

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

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    Yeh the 3LN1 carbies are a different setting to the 3LN3 which is what I have. I'd ensure the needles are stock then richen it in 1/4 turns and see if that makes a difference. Still reckon it sounds lean, rich will be really boggy if it is really bad (doesn't sound like that based on what you described) or will be boggy in places but pull through a bit when you rev it.

    lean will run great up to a point then just struggle to go further because there's not enough fuel in the mix to power the higher RPM.

    With all that said you could also have an electrical problem with the coils or weak spark... so snip 10mm of each of your plug leads if you haven't already and screw them back together.
     
  11. logan anderson

    logan anderson Active Member

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    being that's higher in the rev range would it be better to move needle notch and see if that has an impact?
     
  12. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    Changing the notch on the needle will have an effect at all RPM, as the needle/slide are lifted up by engine vacuum,
     
  13. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    If it's too rich up top you should be able to back off the throttle a little and it'll start to pick up a bit, you can sort of hear it popping in the exhaust

    I wouldn't be playing with the needle clip, carb's need to come off to do that

    Try warming up the engine so it's about 1/4 on the temp gauge, then turn all 4 mixture screw's out 1/4 turn,
    if the idle speed rises, then just turn the idle speed adjuster back out till it idle's at around 1600rpm
    Then take it out for a ride, you'll soon know if it's better or worse then go from there.
    If it help's turn the mixture screw's out another 1/4 turn and adjust idle speed and try it out again till you get it right.
    When you get it close then you can adjust the mixture screw's by 1/8 turn at a time

    One thing i have used on my FZR is an Infrared non contact temp gun, aim it at the exhaust pipe's near the flange at the head and check what temp the pipe's are
    When my mixture's were lean the temp of the pipe's was around 170-180 degree's C, now that it's running good the temp's are over 200 degree's C

    This is similar to the temp gun i have 9mine does up to 500 degree's C)
    https://www.ebay.com.au/itm/Meterk-...080869?hash=item21302b8b65:g:4~sAAOSwpkFY5MI0
     
  14. logan anderson

    logan anderson Active Member

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    Ok, so the twat that rebuilt the carbs messed up and put the main jet and the starter jet the wrong way round on one carb and found the old washer and seal for the mixture screw in the number 3 carb in front of the screw..... which explains so much.
    So after a morning chasing some unfounded goblin that stopped it from firing she now pulls like a train. Still a few hiccups above 10k and some smoke towards redline, but I'll chase those another day
     
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  15. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    So you hadnt even pulled the carbs apart till now ?
     
  16. logan anderson

    logan anderson Active Member

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    Yeah, I was the beformentioned twat sadly.
    Unfortunately i never thought to check my work everytime I've had them opened since.... till now
     
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  17. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    I guess that's where the little phrase about assume comes in handy - glad you got it sorted
     
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