Balancing or synchronising the throttle bodies is without doubt one of those 'black arts'. Last time I did it was on the cafe racer R100 and they were of course carburettor's. All those dials flicking back and forward. Actually a little easier on fuel injection but unless you have the ear of an orchestra conductor you will need something to help you. There are wonderful looking electronic devices available now, but a little too expensive to buy to use once every year or so. I have the Carbtune from Motorworks. Yes a little basic but it works.