Injection Pump
The VP-20 injection pump, mounted at front left of engine, is driven by timing belt. The VP-20 governs injection timing and amount of fuel injected.
The VP-20 injection pump consists of a vane-type transfer pump, pump barrel/plunger chamber, pressure valves, timing control, fuel shutoff valve, altitude/boost compensator, emergency stop lever, and fuel return orifice.
Pressure of fuel (supplied to injection pump) is increased to 36-116 psi (2.5-8.2 kg/cm2 ) by transfer pump (part of injector pump).
A fuel return line allows excess fuel to flow back to tank through a special nipple. DO NOT remove this nipple; it stirs fuel to eliminate wax and ice build-up at pick-up.
High fuel pressure (over 2500 psi (176 kg/cm2 ) is created by closing feed bore and raising piston. Fuel is then distributed to pressure valve.
This high pressure raises pressure valve off its seat, allowing fuel to flow to injectors. Fuel delivery is stopped when control piston reaches full upward travel. At this point, excess fuel is bled back into plunger chamber.