Originally Posted by riikomi

Now I'm happy with my bike. I synced the carbs so that now they are in sync when the throttle is partially open.

Having synced the carbs at idle, the carbs were not in sync in actual driving conditions. When the last transition hole was fully open in carbs #4 and #3, it was only half open in carb #2 and only 1/4 open in carb #1.

So I synced the carbs visually on the table by opening the butterfly flaps until the last transition hole was fully open in each carb. Now the bike behaves well in partial throttle and idles well enough.