But there is nothing wrong with carburetors. If the carburetors are working correctly the engine will run just fine. The only difference you would notice is that a fuel injected motor will run better when the engine is cold. Fuel injection might give it a little more power, but not much more. Fuel ecomnomy will also be a little better with fuel injection.
But there is nothing wrong with a carbureted ZZR600. If the price was right I would not hesitate to get one if this was the type of motorcycle that I liked.