Capacitor start motor is humming?

Brushes are worn out. Take the motor off and get it to a armature shop that rebuild electric motors.

i've got self belief the technical term is "knackered". Discoloured insulation on windings is usually a demonstration of overheating. that would have been brought about by any of fairly some countless issues yet actual, you're watching a re-wind. And the gadget which cuts out the starter winding while the motor is as much as velocity (centrifugal or thermal swap) is likewise suspect. yet your rewinding company will examine that out.

You need what's called a starter capacitor. They're pretty inexpensive. Replace it, and you're good to go. It's hard on the windings to spin-start by hand... Dean

Probably brushes not allowing sufficient current to start the motor.