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FZR250 3LN carb tuning

Discussion in 'Maintenance and Servicing' started by sylvaner, Sep 9, 2012.

  1. Hey guys, I was just wondering if anybody has any experience tuning a FZR250 3ln.
    I have tried many settings but I just cant get it running 100%

    My settings atm are:
    Float Height: 14MM
    Main jet: 42.5
    Pilot jet: 97.5
    Air/fuel Mixture: 2.75 out
    Needle: 2nd highest clip position.
    Mid range to top end needs to be adjusted.

    It seems to be running fine in the lower RPM range so that indicates the floats to be okay, however as soon as I hit around 4k+ the tone of the engine gets lower, almost like its running a tad lean in the upper rev range. From 14K-18K it also sounds a little lean so I'm just wondering if anybody has any suggestions of what to change to get her running perfect.
  2. Is the bike stock or modified?
  3. Hey, the bike is completely stock with good working exup
  4. What colour are your plugs after a good hi rpm run ??

    White = lean

    Grey = OK

    Black & sooty = rich

    Going flat at high throttle settings can be too rich or too lean.

    Its best to try to keep the needle clip in the mid position...having just noticed that you have it set to the 2nd highest position, dropping the needle further into the tube...in effect leaning out from lower mid range...

    Notes for the diagram...ignore straight diam,throttle valve cutaway and needle taper. These are parameters that you are not going to change.

    Main ones are the interaction between air screw/slow jet, clip position and main jet

    Attached Files:

    • Like Like x 1
  5. Not sure on your description here. Is the clip in the 2nd slot counting down from the top, or counting up from the bottom? If it is counting up from the bottom, and the needle is raised nearly to its highest setting, then you will require larger main jets.
    If the clip is in the second slot down from the top, then move the clip towards the bottom of the needle (the pointy end) to richen the mixture.

    Edit. Get your jetting right at wide open throttle first. Top end of the rev range. This is achieved with the main jets. Then fine tune cruise/midrange with needle jet clip position and taper profile. Work back from there
  6. Thanks For the replies guys.
    I did have the needle in the middle position but after the engine was warm it sometimes flooded when taking off from the light, it would take Atleast a few mins to start back up again. I thought this would be the needle since it happened around the mid rev range. As soon as I moved the needle back one space (or closer to the back of the needle) the mid range leaned out and the bike is now completely reliable. I think the bike is now running a tad Lean now so I want to richen is up without having it flood on me. What would be the best thing To adjust?
  7. As can be seen from the diagram below, idle mixture ( pilot air screw ) influences the whole throttle range

    Attached Files:

  8. Just learned from http://fzr250.com/viewtopic.php?t=327

    Pilot screw setting is 3 turns from fully in, which would make your 2.75 a little richer than std.

    ???? needles back to standard mid position, idle screw 3 turns out..and start from there ????

    There is also a copy of the japanese workshop manual on the site( for what its worth, pictures??? )

    Main site, worth a look??
  9. Thanks for the information mike8863, I am aware of the mixture being 3 out, I was just playing around with my settings to try and stop my carbies from flooding. I am a member on the main site but the site has a very low traffic of users so advice is very limited and can take a while to get replies. I was mainly posting a topic on Netrider to see if anybody has had experience with the FZR250 and would be happy to post their settings.

    Damn Japanese workshop manuals ;P

    I will have another play around tomorrow, perhaps taking the needle back a clip to center it again. I'm sure there is another way to stop the flooding, it just takes time to test things out.