MIKUNI CARBS, Part 1: EXPLODED VIEW, with pics

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:




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:





Here's the TOP with everything out:



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.





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




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.

 

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

 

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.

 

Beautiful Fitz! I just rebuilt my Mikuni BS34 & this would have saved me some effort!

 

Great pics Fitz

It's interesting to see the differences with the 32s

 

Nice work Fitz, this should help

MN

 

nice pics! need some hitachi action next

 

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

Big thanks, bigfitz!