Fuel injection pumping apparatus

A fuel injection pumping apparatus comprising a rotary distributor member defining a bore including a reciprocal pumping plunger, a cam member for effecting reciprocation of said plunger in said bore to provide a pumping action on rotation of said distributor member, means mounting said cam member for limited rotational movement during rotation of said distributor member and means controlling said limited rotational movement of the cam member to control the injection pressure characteristics of the apparatus, said controlling means comprising a first cylinder, a first piston in said first cylinder, connection means between said cam member and said first piston, said connection means urging said first piston towards one end of said first cylinder as a result of a reaction force established between said cam member and said plunger during a pumping stroke of said plunger, a second cylinder having one end communicating with said one end of said first cylinder and having its other end open to atmosphere, said second cylinder including a second piston and resilient means in said second cylinder, said resilient means urging said second piston towards said one end of said first cylinder and resisting movement of said first piston towards said one end of said first cylinder until said reaction force increases sufficiently to overcome the force of said resilient means to effect movement of said first piston and movement of said cam member in the direction of rotation of said distributor member and said first piston and said cam member being moved in reverse direction under the influence of said second piston and said resilient means when said reaction force decreases below the force of said resilient means.