To provide a fuel system in which a valve member is speedily engaged with a seat.

A fuel injection system has a fuel pump 10, a spill valve 11 and an injector 12 provided in a sigle unit. The injector 12 includes a valve member 21 biased towards a seating by a coiled compression spring 23. The spring 23 is engaged between a spring abutment 25 of the valve member 21 and a piston 27. The piston 27 is arranged such that the face thereof facing away from the spring 23 has fuel applied thereto when the spill valve 11 is opened in order to assist movement of the valve member into engagement with the seating.