Isochronism:

A governor is called to be isochronous if equilibrium speed is stable for all of the radii of rotation in the working range. Hence, for an isochronous governor the speed range is zero and this kind of governor will maintain constant speed.

Hunting:

Whenever there is modification in speed because of the change in load on the engine, the sleeve moves towards the new location but due to inertia if overshoots the wanted position. Sleeve then moves back although again overshoots the wanted position because of inertia. This results in setting up of oscillations in engine speed. If the frequency of fluctuations in engine speed coincides along the natural frequency of oscillations of the governor, this results in enhance of amplitude of oscillations because of resonance. Then, the governor tends to intensity the speed variation rather than controlling it. This phenomenon is called as hunting of the governor. Higher the sensitiveness of the governor, the difficulty of hunting becomes more keen.