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Mikuni Turbo Carbs

Discussion in 'XJ Technical Chat' started by Fuller56, Mar 30, 2021.

  1. Fuller56

    Fuller56 Active Member

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    Looking for thoughts from the Collective. I have been e-conversing with Hogfiddles and Simmy about these carbs. They are from a Turbo that has only 2631 miles showing on it's odometer so that makes me think it has always had issues. The last fellow to own it spent A LOT of money trying to get these sorted without success. The initial symptom is the bike filling the sump with gas which leads one to believe the floats and needles are at fault which I agree with, especially with the carbs on the bench.
    Hogfiddles has sent me photos of the floats of an unmolested set of Turbo carbs and they agree with all the info I can find in manuals, videos and correspondence. Float height should be 17.5 mm and the physical appearance is that everything should appear level, or very close to it and the adjustment tab or tang should be parallel and level at this setting. Mine are neither. To get the float height at spec the tab is bent way up (carbs inverted). I can have one setting or the other. Attempting to by pass the measured float height and just wet set results in either the fuel level about 1/2 filling the bowl or running copiously out the carb throat. The float valves and seats have been replaced prior to it coming home with me and appear new. I am wondering if they are the correct parts for this model carb.
    Attached pics should show what I am dealing with.
    Thoughts anyone?
    @hogfiddles, @Simmy
     

    Attached Files:

  2. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    Where, on the float, are you measuring? Your “top line” is the crest of the round part of the float. First and last pic don’t look too far off..... middle two are are way low.

    dfox
     
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  3. Franz

    Franz Well-Known Member

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  4. Fuller56

    Fuller56 Active Member

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    Dave, measuring at the apex of the curve. The middle 2 measure out at about 22 mm as pictured.
    Franz, I believe the floats to original by the "patina". The PO reported he and his mechanic discussed replacing them but did not, they did replace the float needles and seats. I am wondering if they are the right parts, too long for application.
     
  5. Franz

    Franz Well-Known Member

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    I have been looking more into the floats, yes I think they are the right ones you have John, float needles and seats possibly incorrect.
     
  6. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    May very well be the wrong fuel valves. Pull one out and measure things, and then tomorrow evening I’ll pull one out and compare
     
  7. Simmy

    Simmy Well-Known Member

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    It could be some different float needles & bodies installed.
    I've attached a pic from the 2 types I've found installed in FZ600 carbs, they are both bottomed out.
    Bend the tab as needed, I don't see why they can't work.
    float needles.JPG
     
  8. Fuller56

    Fuller56 Active Member

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    Thank you Gentlemen. I will shortly go pull out a valve and measure it.
     
  9. Fuller56

    Fuller56 Active Member

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    The overall length of the valve seat is 20 mm including it's filter cap. From the rim of the opening to the shoulder that sits flush with the carb body is 8 mm.

    I could be over thinking this. I suppose I could just continue the wet set procedure and not worry about how it is supposed to look. But then again that has not worked on this bike in it's history.
     

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  10. XJ550H

    XJ550H Well-Known Member Premium Member

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    are the valve bodies different lengths or are the needles shorter than each other.
     
  11. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    I will pull one apart tomorrow evening to compare

    dfox
     
  12. Fuller56

    Fuller56 Active Member

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    No, all are the same and all are new per the PO. Floats appear to be original.
     
  13. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    Floats look correct. I’ll open mine again tonight
     
  14. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    2778E54E-8F6C-49DE-B1D0-AB5F76DAE76E.jpeg


    3F622D44-3A64-475C-A9E0-CA0DAC9AAFC1.jpeg

    9C7157FC-BF90-4FCE-8499-4DA2CEB3CE91.jpeg

    75B749AB-26A3-4750-99B0-633947A0EDA6.jpeg
     

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