Next step to tackle before reinstalling the carburetors is to remove the intake boots and replace their o-rings. The intake boots themselves and the o-rings are a known source of vacuum leaks in the intake system. The original intake boots still look good. No visible cracking and the rubber is still supple. I have heard of people having a difficult time trying to remove the boots since they have usually been in place for so long in a high heat area. The screws have JIS #3 heads which most people attack with a regular Phillips head screw driver until they strip the screw head and then end up trying to cut a new slot in the head to use an impact driver for removal. These screw heads looked OK and I had both a JIS #3 screw driver and a JIS #3 bit for my impact driver to hopefully avoid some of these removal issues.
Here are the intake boots before removal:
I gave a halfhearted attempt to remove them early on when I was working on the valve adjustments and was able to remove 3 of the 8 screws. I sprayed the remaining screws with Liquid Wrench and left it alone until today. Today I was able to remove all but one screw and that one came off quickly with the impact screw driver.
As mentioned, the intake boots seem to be in good shape, but the o-rings were a different story. The o-ring on intake #3 was visibly cracked as shown in the red circle and the other three were hard as a rock. These vacuum leaks could have caused hard starting and hanging idle with the lean fuel mixture that would be created by additional air being sucked into the fuel mixture before entering the cylinder.
Here is the result of removing the petrified o-rings along with the new o-rings and new SS Allen head bolts to remount them (the full o-ring kit for the carburetor o-rings and the intake boot o-rings and the SS replacement bolts come from http://cycleorings.com/):
Putting them back together, I used silicone grease (Uncle Walt switched me over to the Dielectric Tune-up Grease from the silicone lube that I had been using on the carburetor o-rings) to help hold the o-ring in place, improve the seal, and maybe increase the lifespan of the o-rings and put some anti-seize compound on the new screws.
Back on the bike with the new screws: