The results of the author's previous report showed that the linear approximation considering a phase lag of the subventuri pressure surely predicts the instability of an equilibrium state except at extreme lower speeds, and gives the hunting frequency almost correctly ; but the calculated value of the increment of amplitude at the largest hunting state differs from that of the nonlinear simulation. For a better understanding of hunting, it is desirable to be able to get the amplitude and frequency of hunting analytically. As a first step toward nonlinear approximate analysis, in the present report is made clear the effect of individual parameters of a closed-engine-governor system on the instability of equilibrium state, i.e. increment of amplitude and frequency on the basis of the linear approximation. The results show that the moment of inertia of crankshaft system and the constant relating the developed torque to fuel rack displacement, in addition to the phase lag of subventuri pressure, exert a marked influence on the instability, but the constant relating the torque to the engine speed does not affect so much, and that the damping of the governor system does not stabilize the closed system but affects the frequency, whereas the mass has an effect on the increment of amplitude but does not affect the frequency.