Fuel injection pump having variable prestroke mechanism

A fuel injection pump comprising:

• a reciprocating plunger for injecting a fuel from a fuel reservoir into a fuel injection chamber, said plunger having a fuel passage means extending therein including one end thereof open to the fuel injection chamber and another end disposed in the fuel reservoir;
• a control sleeve extending around said plunger and in which said plunger is slidably mounted, said control sleeve having a cut-off hole extending between the plunger and the fuel reservoir,
• said plunger sliding over a first distance in a first direction within said control sleeve from a first position at which said another end of the fuel passage means is open to the fuel reservoir to a second position at which said another end of the fuel passage means is closed by the control sleeve so that said plunger initiates the injection of fuel into the fuel injection chamber, said first distance representing a prestroke of injection,
• said plunger sliding over a second distance in said first direction within said control sleeve from said second position to a third position at which said fuel passage means is open to the cut-off hole to place the fuel injection chamber in communication with the fuel reservoir chamber and terminate the injection of fuel into the fuel injection chamber, said second distance representing an effective stroke of injection;
• adjusting means for adjusting the radial position of said control sleeve relative to said plunger to vary said effective stroke from a predetermined value;
• and
• said control sleeve also having a connection port open to the inner surface thereof for discharging fuel from the fuel injection chamber therethrough prior to the termination of fuel injection when the effective stroke is varied by said adjusting means to be higher than said predetermined value.