Finally getting started on the carburetor rebuild. The plan is to tear down each of the carburetors, put all of the metal bits into a carburetor cleaning bath, make sure all of the jets and body orifices are clear, and replace all of the o-rings within the carburetors and the intake boots with an o-ring kit from http://cycleorings.com/.
The carburetors on this motorcycle are Mikuni BS32SS which are very common to this generation of motorcycle. A couple of nice reference documents are available online to supplement the information in the service manual and parts diagrams. http://zeus.mtsac.edu/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf and http://zeus.mtsac.edu/~cliff/storage/gs/mc_maint/GS_CV_Carb_Cleaning_Series.pdf.
Here are the carburetors as removed from the motorcycle:
Carburetors removed from the rails and pulled apart:
It is fairly straightforward to breakdown the carburetors. The most important advice is to have properly fitting screwdrivers. The screws that appear to be Philips head are actually Japanese Industrial Standard (JIS). I have a good set of JIS screw drivers and impact driver bits that you can find here, http://www.vesseltools.com/. The jets require slotted screw drivers that must also fit well. For the main jet, I filed down a 5/16″ screw driver blade until it fit just right as you can see in the photo below.
The red circle above is the only screw that gave me much trouble on Carburetor #1. This screw holds the plate which retains the needle valve. Quite a bit of corrosion there. I tried carb cleaner and penetrating fluid until I was afraid that I would strip the screw head. Turns out a couple of taps on an impact driver with the JIS #2 bit loosened it right up.
Here is Carburetor #1 broken down and ready for dipping. Quite a few small parts to manage.
Doesn’t look too bad, but there are clogs that you can find when you try to spray carb cleaner into an opening and the spray does not come out where it is supposed to… I am going to try an initial bath of 2 hours, put this carburetor back together with the new o-rings and gaskets, and then continue with the other carburetors one by one.