Bill,
Was anything at all done to the motor, ignition, wiring harness or any other variable from the last time the motor ran correctly?
Check the ignition pickup and rotor. Pickup to make sure its not pulling away from the rotor and the rotor to make sure it's indexed correct and not loose. It's tough doing a "over the net" diagnosis.
I would be more then happy to help you diagnose this, its just a little hard with only given what you gave me. Shot me an instant message or email and I will try to help you figure this out.
Best of luck,
-Buzzy
