In addition to what was said above, some motors have start and run capacitors. The centrifugal weights remove the start capacitors as the motor gets up to speed. A run capacitor stays in the circuit while the motor is at speed. Without a run capacitor you won't get much torque. With a heavy load on the motor the run capacitor gets a workout (as well as the motor windings) and can be damaged. All this is why many small, inexpensive, electric motors are junked when they quit as it can be hard to determine the exact problem without spare parts and experience to guide you.
What he Said!
I would suspect the Capacitor. You can get them from grainger. See if there is a frame size on the motor and also the rpm on the nameplate of the motor. I have quite a few motors and could most likely match it up and probably have a 3/4 hp that may fit. Just the cost of shipping if I have it.
I changed a lot of my equipment over to VFD drives and three phase motors (115 v in 230 v out) and i have the belt set at the highest speed and controll from the vfd.