New Holland CX720 Repair Manual page 1859

POWER PRODUCTION - FUEL AND INJECTION SYSTEM
Because the end of delivery is reached when the helix on the plunger uncovers the spill port (1) the amount of fuel
delivered is varied by turning the pump plunger as shown at (D). If the plunger is turned until the vertical groove
completely uncovers the spill port as shown at (E), during the entire lift of the plunger, there will be no fuel delivered
to the engine. This is because injection pressure cannot be reached, thereby shutting off the engine.
The plungers are rotated by a control rack splined to each plunger. Rack movement is determined by the control rod,
actuated by the governor.
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Fuel Delivery and Timing During Starting
The plungers (1) are equipped with starting grooves (2) on their crown. The purpose of this groove is to assist in
starting the engine by providing both excess fuel and slightly retarded timing. When the key switch is turned on,
the fuel shutoff solenoid retracts, moving the mechanical shutoff lever to the "RUN" position. The starting spring in
the governor housing pulls the control rack fully forward, beyond the normal maximum fuel position. This aligns the
starting groove with the spill port. With the starting groove aligned with the spill port, there is a delay in spill port
closure which, in turn, delays the start of injection. Note also that there is no helix in this region of the plunger, so
once injection begins, it is not cut off until the plunger reaches the end of its stroke. This provides a very large amount
of fuel to aid starting.
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Delivery Valves
A delivery valve is located above each plunger. The delivery valve serves as a one-way valve which allows fuel under
injection pressure to move into the high pressure tubes and prevents fuel from coming back. The valve also serves to
rapidly reduce pressure in the injection line once pressure from the plunger has ceased. Rapid pressure reduction is
required to ensure the injector valve snaps shut to prevent fuel "dribble," a condition which can cause carbon formation
on the injector tip.
(a) Valve closed
(b) Valve open during fuel delivery
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