I've synchronized carburetors before, but I'm not familiar with the Keihin carburetors on my 78 cx500. How do you adjust the slides while the bike is running to synchronize them? It looks like the slides are raised by vacuum. Thanks for your help.
You are not trying to adjust the slides, but adjusting the butterflies to open exactly the same amount. When they are properly adjusted, the slides will follow suit.
There is an adjustment screw and lock nut on the linkage between the two carbs. Turning this screw changes the relationship between the two carb butterflies. It doesn't take much sometimes to make a large vacuum change. Even a 1/16th turn can make a big change. I would recommend using a Morgan Carbtune for your gage, but others have made their own and been successful. Calibrating the two gages is important before you begin. If they don't read exactly the same under a given vacuum, you will be chasing ghosts.