Help a newbie? Ignition trouble, '82 kz1000

Hey everyone--I just picked up an '82 KZ1000 CSR a couple days ago. It ran fine at the other guy's place, but hasn't since. First, it wouldn't start and the battery seemed low, so I cleaned up some ugly wiring off the negative post, and gave the battery an overnight charge. Then today, still wouldn't start. I pulled the plugs, they were black and wet. What's more, they still had the little caps on the ends! (That blew my mind.) Put in new plugs and it fired right up. So I took for a five minute spin, but it felt like it was going to die the whole time. I kept it alive by never fully letting go of the throttle, got it home and parked it.

So then, it immediately dies, and on repeated starts won't stay running. I pulled the plugs (which were hot!) and found them already totally black.

The bike's got yellow Accel coils and wires, by the way.

Any advice? Thanks.

-Steve

Another clue: when the motor dies there's a brief skittering sound, like you slid a tin can on the sidewalk. ???