Generator speed control by amperage draw.

For an induction motor to operate as an induction generator, it has to always operate above synchronous (not base) speed. Always.
Additionally the power output peaks at about 3% positive slip. Anything above or below, and you rapidly lose power capacity.
For a 4 pole motor operating at 60 Hz, this means a maximum speed of 1854 RPM.

The optimal operating condition is thus to drive the motor at that speed continuously, and allow the load to draw whatever amount of power needed. Don’t attempt speed control unless you measure real power, watts, not apparent power, VA and have a way to ensure that the load current doesn’t suddenly change 180 degrees, meaning that your generator is actually consuming power.

Also, induction generators require a primary excitation voltage at the correct frequency. I have seen people obviate this requirement with a three-phase motor and resonant capacitance, but only drawing power from a single phase.

Lastly, induction generators cannot produce reactive power, you would have to ensure that your load has unity power factor.