Cleaned the carbs this morning. My CBR uses Keihin's. First I cleaned the piston slides and bores. The pistons are plastic and they seem to get varnish on them, which prevents the slide from moving smoothly. I ride the bike almost every day, even during the winter. After doing the slides, I sprayed carb cleaner through the air passages, and held open the choke and sprayed through there. I use some Vaseline in the groove that the lip of the diaphram seats, to hold it while I put the spring and cap over the diaphram.
After doing all four slides, I tested the pistons by lifting them up and letting them fall. Worked much smoother and fell with a snap instead of a thud before cleaning. Then I turned the carbs over and cleaned the float chamber jets and set the floats. One was low.
The worst part was taking off the 32 phillips-head screws. Only two of the 32 have hacksawed-slots where I've stripped the heads. I use my left hand to turn the screwdriver, while my right hand, right shoulder, and right chest push down on the screw. The bike worked great afterward. Here's a picture showing how dirty the piston slide was.