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Help FZR250 3LN3 carb problem.

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

  1. driftwood

    driftwood Well-Known Member

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    I'm losing it. 0.3mm goes in
     
  2. Gert

    Gert Well-Known Member

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    Recieved the seals. Thank you Blair, took a while, but better late than never.

    [​IMG]

    Anyway, adjusted fuel level a bit, but as expected, not enough. Rised fuel level another bit and almost good.
    There was an lean spot at about 4.000 - 6.000 rpm so I raised the needles one notch.
    Now she has fuel enough, perhaps a bit too much. Dunno.

    The bike starts good now when cold with choke and soon I am going to drive around and see how she handles on the street.
     
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  3. Gert

    Gert Well-Known Member

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    Drove around and pickup from closed throttle is still a tad too lean. I am not happy with it.

    So I dropped the needle one notch to original place and raised fuel level a bit. Result was a tad better but not perfect.
    Finally I turned the mixture screw one turn more out and now it became like it should be.
    I noticed that one carb fuel level differs from the rest, so I am going te fix that.
    Measure A/F again and than I hope it is finished.

    In the mean time, I have removed and installed the carbs hundreds of times now. If there is ever going te be an competition in removing 3LN carbs, I think I make a good chance :)
     
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  4. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Good work Gert. Two questions: did you see the work that My67xr did to get his FZR running on song, and did you originally set the pilot mixtures by ear or 'n' turns out?
     
  5. Gert

    Gert Well-Known Member

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    Started with base settings: 3 turns out.

    I did probably read My67xr work, but I don't know what you are referring too?
     
  6. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    I just mean the process he went through of experimenting with fuel height and settings before he was finally happy. The best fuel level he got was the oem setting.
     
  7. Gert

    Gert Well-Known Member

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    Good to hear people are able to receive oem setting.

    The first time, years ago, when the engine quit running, I started cleaning carbs etc. When that did not help, I changed fuel level by bending the float lever a little. Since that moment, oem setting is useless, I am afraid.
    Oem setting is only achieveable with stock floats, without messing with the lever at all.

    So, for me, the only way to get a nice running engine is measuring fuel level, measure A/F, listen and test the bike.

    Anyway, I tried to get oem level and measure like described. But I am getting nuts how to do that. Where do I measure exactly? In the middle? Side? Top? Left? Right? So, for me, to dumb to measure float level, I simply measure fuel level and see what happens.

    It was too late last night to finish, but first impression, with an pretty high fuel level and the mixture screw a tad more than oem, she did sound really nice and idle was good too. I had a big grin on my face.
    I am eager to build her up and go for a drive.
     
  8. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Hi Gert,

    I'm writing this with other forum users in mind also, so apologies if it's too simple, trying to consider that people with no experience will also read this post as the audience.

    So I will provide a few links - verification that the correct fuel level for the 3LN3 is 10.5mm for best performance AND that should be a measured float height of 14.7mm
    https://www.2fiftycc.com/index.php?threads/my-fzr250-3ln6.10959/page-2#post-136440

    Now the float height obviously affects the fuel level, sorry not trying to be too simple, what we have found is that for the FZR250 - float height in millimetres, PLUS fuel level in millimetres usually equals 25.2mm

    SO
    Float height = 25.2mm - fuel level; and
    Fuel level = 25.2mm - float height
    As one increases, the other decrease

    These may not be absolutely correct in all circumstances, you need to adjust float height to get the correct fuel level.
    Fuel level is the important measurement and float height is the adjustment.

    Pretty picture of the device @my67xr made to measure float height
    https://www.2fiftycc.com/index.php?threads/my-fzr250-3ln6.10959/page-2#post-136441

    The way I did it - with a playing card - that 16mm measurement is for the 3LN1 - they have a float height of 16mm which gives a fuel level of 9.2mm
    Remember
    yours is a 3LN3 - as above float height should be 14.7mm and as a result of setting that correctly, the fuel level should 10.5mm - remember they both add up to 25.2mm

    Note - the second picture is the fuel level measure - sorry the picture is blurry, and there isn't any fuel in the tube and syringe, but you can just see the line on the carburetor float bowl to take the fuel level measurement - this should obviously be done with the carbs on the bike.

    https://2fiftycc.com/index.php?threads/my-fizzer.872/page-32#post-15537

    This is a very ingenious way to adjust the float tang as it needs subtlety, more cleverness from @my67xr
    https://www.2fiftycc.com/index.php?threads/my-fzr250-3ln6.10959/page-3#post-136538

    After each adjustment, swing the float and recheck the measurement.

    Now as to measurement and adjustment of the float height, if you have the float bowls off, carbs upside down, you can tilt them and see when the floats stop swinging as you turn them

    You basically want to find a way to have them on a table in front of you, stable in that position to measure and adjust.

    When you have all of the float heights at 14.7mm, reassemble put them back onto the bike, bike level and upright, a rear paddock stand will lift the back and have a tiny affect on the measurement, probably less than we can actually see though

    Key on, pump fills carbs, clear hose on the drain hole(s) or - take measurement(s) - remember the bottom of the meniscus is the measurement line

    Now if you need adjust the fuel level via the float height:
    higher fuel level = lower float height
    lower fuel level = higher float height

    It probably took me longer to write this than to check and adjust all 4 floats to get them correct
     
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  9. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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  10. Gert

    Gert Well-Known Member

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    Ruckusman, thanks for your excellent answer an patience.

    Anyway, on my bike it did not work.
    Setting the carbs in oem way was creating a lean spot. The only way to tackle that, was lifting fuel level a bit and 3/4 turn more out for the mixture screw.
    Installed everything now, but I did not have the time to test on the road.

    For chronology:
    In 2016 the engine quit running.
    Found this site, Blair and Keyster: bike running again.
    Swappet float needle, emulsion pipe and needle, new gaskets and an overall clean up.
    But she never ran like I hoped. Cold start was bad too.
    So, this winter I decided to get me some oem emulsion pipes and needles and try to get her better running.
    Unfortunately, emulsion pipes available, needles not!
    So, swapped emulsion pipes and installed the old oem Mikuni needles.
    Hmm, engine would not rev anymore passed ± 6000 rpm. And blipping the throttle was not good either. Measured with an wide band A/F analyzer = lean spot.
    Swapped the old Mikuni needle with the Keyster one.
    Nothing changes.
    Raised fuel level: tiny bit richer and better running.
    But still not good enough.
    Swapped the needles again and Mikuni's back in the carbs.
    No changes.
    So, raised needles one notch (= 0,5 mm?).
    Now, pretty good. Took her for a spin, measured A/F, pretty rich, but good.
    But still, I was not satisfied with throttle pickup.
    So, turned out the mixture screw a little. That went better.
    Finally, dropped the needle in the stock middle position, raised fuel level a bit and mixture screw set at 3¾ out.
    Tested, measured and listened. She runs good, aggressive on the throttle, but pretty rich.
    Better rich than sorry.

    Okay, just a afternoon test drive on the streets left to do, I am curious.

    Checking fuel level:
    [​IMG]

    Connecting sensor:
    [​IMG]

    Idle A/F:
    [​IMG]

    Checking temp headers (not easy to shoot left with the gun and right with the camera, simultaneously):
    [​IMG]
     
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  11. driftwood

    driftwood Well-Known Member

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    I'm still running poorly, but got my Roadworthy yesterday. With a new pair of Angel GTs, I can do some roads so as to get motivated some more. Thanx to all here.
     
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  12. Gert

    Gert Well-Known Member

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    Bummer, drove around and still no good, so I pulled the carbs again. These things are driving me crazy.

    Adjust everything to exact stock settings and started the bike. Still no good, so actually, it must be something else. So perhaps an air leak?
    So I sprayed some brake cleaner between the carbs and the intake rubbers. The engine started to idle lower and finally stalls... hmmm... not good.

    Nothing to see on the carbs and the intake rubbers are good too, at least no visible damage.
    So, what to do? I notice that intake rubbers are still available (I think), but they cost a fortune.

    Tips anyone, before I burn my wallet?
     
  13. driftwood

    driftwood Well-Known Member

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    My 3LN6 boots need full body weight on one side at a time, with rubber lube, to push carbs home.
    Two of mine run rich, so much so that I'm keeping it on the boil at 7k+ to avoid fouling (funny experiences: a GSX-R thought I was taking him on as I wound it out leaving the lights etc), tho idle is acceptable at 2k. Stumped. At least starting is instantaneous!
    Can anyone supply the cross-section diag for a BDST so that I can ponder if the choke circuit is the issue?
     
  14. Aaron81

    Aaron81 Active Member

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    FWIW When dealing with troublesome jets I found a set of Oxy cleaning tips to be a god send!
     
  15. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Just a comment Gert.
    The A/F is going to be useless, except for idle, unless you can mount it to the bike and check while riding.
    I don't believe in "better rich than sorry". It's a 4 stroke. Your bike will be running rich like every other Japanese bike with carbs. Except for one of the punters here who races an MC22 and runs smaller mains.
    Rich = destroys your rings and makes it run like a pig.

    So I sprayed some brake cleaner between the carbs and the intake rubbers. The engine started to idle lower and finally stalls... hmmm... not good.

    The solvent definitely found its way into the inlet via the boots and not through any of the carb vent tubes or throttle shafts?

    Having said all that FZR250's are somewhat notorious for carb issues. Which is why I started on this process with the help of a forum member. Stalled now until I get my own FZR.

    [​IMG]
     
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  16. Gert

    Gert Well-Known Member

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    Yes I can. See pic earlier taken:
    [​IMG]

    I do believe in "better rich than sorry". I have seen several melted pistons due to a lean mixture. Not good, my 3S-GTE piston:

    [​IMG]


    Anyway, about my carbs. I will remove a boot and take a close look and see if there is anything unusual. I saw that Ali is selling FZR250 boots from BJMOTO for fearly cheap, anyone any experience with those?

    A vacuum leak could explain why the engine stalls sometimes and not an steady idle.
    I am sure the carbs are clean and all settings and jets are oem specs. There must be something else wrong.
    Keep you posted!
     
  17. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    It has been reported that the Chinese boots last 12 months before starting to crack.
    3S-GTE say whaaaat? We can't let you sneak forced induction into the argument, that's cheating. :)
     
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  18. Gert

    Gert Well-Known Member

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    Okay, this one:

    [​IMG]

    And this one:

    [​IMG]

    :)

    But that is cheating too. First one is from Aprilia SX125 and second one from Aprilia RS250, both two stroke.

    Too be honest, I tested A/F with the MC22 and the MC22 is much more richer than the FZR. Stock MC22, except the bolt on (loud = open) muffler.
     
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  19. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Silly question, but this caught someone else out - boots tightened securely onto the cylinder head?

    Chances they have micro cracks, but it's sometimes the simple things which get missed
     
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  20. Gert

    Gert Well-Known Member

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    Removed one boot for an close inspection. Nothing wrong with it, seals good to the head and fits perfect to the carb.
    I am afraid it is not in the boots.
    Probably have to replace the throttle shaft seals. Bummer :-(.
    Find me some JIS tools and a small dremel and an rebuild kit, Blair?

    This evening I will try to discover some more about the vacuum leaking.
     

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