What did the plugs look like when you changed them? Were they black or white? ALso, when the bike is up and running, what temp does it like to hang around? Rich running bikes will blacken the plugs and make the bike run cooler.
IF the bike is new to you, I'd take the carb apart, tear it down, check floats, unscrew all the jets and make sure they are really clean. Then follow directions above. Syncing the carbs can be a pain in the ass - if you don't feel like buying vacuum gauges, you can accomplish the same thing with some 3/8 plastic tube taped in a loop around a yard stick - there has to be a pic of tha ton here somewhere. Good luck!
02 Yellow zx-6r
Full akra exhaust, lowered, some other aesthetic shit