Wont Run unless hold start switch

You most likely have a faulty motor centrifugal switch. This switch is engaged when the motor starts rotating. The switch itself could be faulty or the inertia-mechanism that activates the switch could be faulty. The inertia-mechanism usually has two small springs that pull it back into its resting position when the motor stops turning. I have found that the springs will sometimes break and produce the symptom you have described.

Below is a diagram of common centrifugal switches. The switch will be mounted on the end of the motor.