An aircraft engine fuel system, comprising: a metering valve having inlet and outlet sides (21,22) and being configured to monitor fuel flow from the inlet to the outlet side; a check valve arranged, when open, to allow fuel to flow toward the inlet side during start and climb conditions and, when closed, to prevent such fuel flow; and an ejector pump, which is operably disposed between the check valve and the metering valve, and which, with the check valve closed, is configured to pump fuel toward the inlet side of the metering valve during idle conditions; and a pressure regulating valve to restrict fuel flow from main and auxiliary pumps (30,40), which are disposed to pump fuel to the inlet side in accordance with a pressure differential between the outlet side and fuel pumped by the auxiliary pump, the pressure regulating valve comprising: first and second connected piston heads (51, 52) elastically anchored to a first valve end and biased toward a second valve end, the second piston head having a groove that fluidly communicates with a conduit by which excess fuel pumped by the auxiliary pump is bypassed from the inlet side with the first and second piston heads moved toward the first valve end by a first distance from the second valve end; and the first piston head having a groove that fluidly communicates with a conduit by which excess fuel pumped by the main pump is bypassed from the inlet side with the first and second piston heads only moved toward the first valve end by a second distance from the second valve end, which is larger than the first distance. a metering valve having inlet and outlet sides (21,22) and being configured to monitor fuel flow from the inlet to the outlet side; a check valve arranged, when open, to allow fuel to flow toward the inlet side during start and climb conditions and, when closed, to prevent such fuel flow; and an ejector pump, which is operably disposed between the check valve and the metering valve, and which, with the check valve closed, is configured to pump fuel toward the inlet side of the metering valve during idle conditions; and a pressure regulating valve to restrict fuel flow from main and auxiliary pumps (30,40), which are disposed to pump fuel to the inlet side in accordance with a pressure differential between the outlet side and fuel pumped by the auxiliary pump, the pressure regulating valve comprising: first and second connected piston heads (51, 52) elastically anchored to a first valve end and biased toward a second valve end, the second piston head having a groove that fluidly communicates with a conduit by which excess fuel pumped by the auxiliary pump is bypassed from the inlet side with the first and second piston heads moved toward the first valve end by a first distance from the second valve end; and the first piston head having a groove that fluidly communicates with a conduit by which excess fuel pumped by the main pump is bypassed from the inlet side with the first and second piston heads only moved toward the first valve end by a second distance from the second valve end, which is larger than the first distance. first and second connected piston heads (51, 52) elastically anchored to a first valve end and biased toward a second valve end, the second piston head having a groove that fluidly communicates with a conduit by which excess fuel pumped by the auxiliary pump is bypassed from the inlet side with the first and second piston heads moved toward the first valve end by a first distance from the second valve end; and the first piston head having a groove that fluidly communicates with a conduit by which excess fuel pumped by the main pump is bypassed from the inlet side with the first and second piston heads only moved toward the first valve end by a second distance from the second valve end, which is larger than the first distance.