In a two stroke engine, for every two rotations of the crank

shaft there will be one power stroke.Hence during

compression stroke, fuel will be drawn in to the crank case

(suction) and during power stroke, burnt fuel will be thrown

out through transfer ports (exaust).

In a four stroke engine, for every four rotations of the

crank shaft there will be one power stroke.

Here, suction, compression,power & exaust strokes are seperate

as there will be inlet and exaust valves.