I had a similiar problem on my zx-12 a few years ago. The bike would start and run but as soon as i let out the clutch out it would die. It ended up being the "clutch saftey switch." Apparently its tied to the sidestand switch. Anyway, it the little, spring loaded switch in the clutch perch. I diagnosed it by taking the switch out and cleaning it, reinstalling and problem solved.
Might check this switch.
Huero