I've a ZZR600, 1997, 22K miles. The clutch is notorious for a being a 'clunk' into 1st gear.
I've noticed recently that when I start from cold and pop into 1st gear with clutch in, the rear wheel spins quite vigorously (so I need the front brake on). Once warm, the rear wheel doesn't spin when in 1st gear and clutch pulled in.
I recently changed the clutch cable and oil, and have played with the adjustment on the cable.
Any clues as to what to look at?