Reader's digest version:
When you sync the carbs, you are making sure that all four carbs are pulling an equal vacuum. This adjustment assures that you have a smooth idle, and that the bike is smooth at lower carb openings.
Each carb should have a small vacuum port with a rubber stopper installed over them. This is where you hook up a vacuum gage or a fancy shmancy synchronizer board. With the sync board, you hook up all four at the same time. With a vacuum gage, you have to do one carb at a time.
So, find the vacuum ports, and the adjustment screws. Both of these are usually at the carb inlet, facing up for easy access.
Next, start the bike, let it warm up, and set the idle to the manufacturer's recommendations.
Next, hook up the vacuum gage or board. With the gage, you want to adjust the mixture screw until you pull the maximum vacuum. The needle will jump up and down, so keep tweaking until you get the maximum peak. Write that number down, and move to the next carb. Be sure and replace the vacuum plug once you are done.
Move on to the next carb, and attempt to get the same vacuum reading. You want the same peak reading for each carb, so you may have to go throught the procedure a couple of times. Once the carbs are equalized, you are done.
With the board, you hook up all four carbs to the board at the same time, and maximize and equalize the liquid in the tubes. The board makes the job much easier and quicker. NOTE: don't rev the engine too high with a sync board, as you can pull the fluid out of the board into the engine.
655321 claims no responsibility for the above nonsense, and is a shadetree mechanic at best.