Fuel injection nozzles

A fuel injection nozzle for supplying fuel to an internal combustion engine comprising a nozzle body, a bore formed in the body, a seating defined at one end of the bore, an outlet from said one end of the bore, a valve member slidable within the bore, said valve member being shaped for co-operation with said seating, a passage through which in use fuel can flow at high pressure to act upon an area of said valve member to lift the valve member away from said seating thereby to allow flow of fuel through said outlet, resilient means for opposing the movement of the valve member, an adaptor mounted upon the valve member and which serves to transmit to the valve member the force exerted by said resilient means, a cylinder defined in the adaptor, a plunger slidable in the cylinder, passage means for admitting fuel under pressure to one end of said cylinder, the force produced by the fuel under pressure acting on said plunger opposing the action of said resilient means, and stop means for limiting the movement of the plunger, the arrangement being such that the initial movement of the valve member against the action of the resilient means, is assisted by the action of said plunger, the final movement of the valve member after the movement of the plunger has been halted, being due to the fuel under pressure acting on the valve member only.