Quantitative governing.

* In this system of governing, the quality of charge (i.e. air-fuel ratio of the mixture) is kept constant.

* But the quantity of mixture supplied to the engine cylinder is varied by means of a throttle valve which is regulated by the centrifugal governor through rack and pinion arrangement.

* The part load efficiency of S.I. engine is poor because air fuel ratio remains constant even if we need low power

Qualitative governing. 

* In this system of governing, a control valve is fitted in the fuel delivery pipe, which controls the quantity of fuel to be mixed in the charge.

* The movement of control valve is regulated by the centrifugal governor through rack and pinion arrangement.

* Part load efficiency of C.I. engine is good because we can use lean mixture and rich mixtures easily according to our requirement