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MIKUNI CARBS, Part 1: EXPLODED VIEW, with pics

Discussion in 'XJ DIY How-To Instructions' started by bigfitz52, Apr 24, 2011.

  1. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    Alrighty then fellow Mikuni sufferers, it's time to spread some info on the "neglected" carburetors, the Mikuni BS28s as fitted to the XJ550s, both Seca and Maxim.

    This is part one, containing an "exploded" view, all labeled and diagrammed. Part two will be a step-by-step breakdown of a rack for "basic" carb service; part of regularly scheduled maintenance. Part three will cover throttle shaft seals but it's going to have to wait until I NEED to do some.

    Here we go, an EXPLODED VIEW with everything as close as I could get to having it all fit the diagram:

    [​IMG]


    HOLY CRAP Fitz, where'd ALL THAT stuff come from?

    These components come out of the TOP, once the Hats, Diaphragm Springs and Diaphragm/Slide/Needle assemblies have been removed:

    [​IMG]



    Here's the TOP with everything out:

    [​IMG]

    Note in the EXPLODED VIEW the tiny o-ring and washer on the PILOT MIXTURE SCREW. These generally stay behind and need to be picked out with a hook-shaped implement of some sort, being careful not to gouge up the bore and screw seat in the process.



    These components (and the floats and needle valves, already removed) come out the bottom: Note that the Enrichment Tube is FIXED and cannot be removed.

    [​IMG]



    And here's the bottom, stripped. Again, note that the enrichment feed tube is fixed, and removal should not be attempted:

    [​IMG]


    NOTE in the pics of both the top and bottom "stripped" the locating pin for the needle jet/emulsion tube. Care needs to be taken in both removing and reinserting the emulsion tube so that this pin doesn't get damaged. Use too big of a drift to remove the tube and you could shear it clean off.

    ANOTHER NOTE: The rubber "boot" on the enrichment plunger guide/retainer is currently NOT AVAILABLE* so be very careful with those. There is no need to remove them normally; I took the one off for this article so you could see how they're retained, etc., and since it's new I wasn't worried about tearing it.

    Hope this helps get anybody fighting with Mikunis a bit more to go on. As always, comments or suggestions are welcome.

    More to follow, in Part 2; but there was no sense in waiting for that to get finished.

    Enjoy.

    *UPDATE***This is no longer 100% true. XJ4Ever now carries replacement enrichment plunger boots for most applications. Contact chacal for details.
     
    Last edited: Nov 11, 2014
  2. macros10

    macros10 Member

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    Very nice! I'll have to print this out so the next time I have questions, I will actually know the correct name of the part I'm asking about, lol! Thank you very much for this BigFitz! It will help us fellow '550 and other Mikuni carb owners very much!

    mac
     
  3. Metal_Bob

    Metal_Bob Active Member

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    Great work!

    Definately looking forward part 2.

    I need to clean a set of carbs (not sure which set yet) and check all my cables because I often get high revs at red lights, especially after I get off the highway.
     
  4. KA1J

    KA1J Member

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    Beautiful Fitz! I just rebuilt my Mikuni BS34 & this would have saved me some effort!
     
    buyerz78 likes this.
  5. Desinger_Mike

    Desinger_Mike Member

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    Great pics Fitz

    It's interesting to see the differences with the 32s
     
  6. tabaka45

    tabaka45 Well-Known Member

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  7. MN-Maxims

    MN-Maxims St. Paul Minnesota

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    Nice work Fitz, this should help

    MN
     
  8. mtnbikecrazy55

    mtnbikecrazy55 Active Member

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    nice pics! need some hitachi action next :D
     
  9. FrankBlack

    FrankBlack Member

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    Awesome! Plan on tearing down my carbs next week, this will definitely help!

    Big thanks, bigfitz!
     

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