Starting cap switch is hanging up. Pull the motor apart, take a look at
the switch assembly on the end of the shaft. Odds are good that the
contacts are horribly burned.

JimInsolo wrote:
I have a 1 HP induction motor with capacitor start and capacitor run. As I
understand the function, the start capacitor circuit is engaged at start up
and then dis-engages when the motor reaches full speed. The motor works
fine most of the time, but every so often it will make a terrible sort of
vibrating racket and blow the breaker. Sometimes if I just wait a minute or
so it will start and run fine again. Any ideas on what could cause this?