Bob,

Stepping back for a minute to basic motor theory.

Three phase induction motors produce a rotating magnetic field that the rotor tries to follow. The phases are separated by 120 degrees.

Single phase induction motors produce a rotating magnetic field by altering one of the two magnetic fields by either changinging the stength / phase by adding capacitance or inductance to the field. When the rotor gets up to speed, a centrifigul switch removes the added reactance and the motor keeps running.

A BRUSHED "universal" motor that can run on AC or DC may be a better generator. Get the motor up to synchronous speed, if required, pulse DC through the rotor and I believe you will get a useful output.

Quote
the motor is a squirrel cage induction motor, no capacitor, 4 pole 1400 rpm @50Hz


Isn't synchronous speed for a 4 pole 50 HZ motor 1500 rpm?

Good luck.

Larry