I have a kawasaki GT550 and i bought some vacuum gauges, how do i balance my carburettors?

Ok the basics, it seems you have already. On each carb you have a vacuum port that is normally covered with a little nipple of rubber. Remove these and hook up your vacuum guages. I like to do this while the engine is running and already warm. One at a time. So you are basically adjusting the throttle plate, erfly valve or variable venturi depending on your style of carbeurator, so that all carbs have the same amount of vacuum to the engine at a given point. Now I normally just get the idle set and leave it at that. To adjust throughout different bands in the RPM range is going to affect your main adjustment at idle. Normally the throttle body has a permanent adjustment on the linkage that actuates the throttle, this is done with a screw and nut most often. I do not know specifics for the GT550 however it is similar for most bikes. At various RPM's you can take different readings and turn those into percentage differences in hopes of giving you a median number to tune for at idle if you wish. But lets face it, no 2 cylinders, 3 or 4 are built the same anyways, and unless your building a race engine you don't need to be that crazy.