Abstract: A flow control unit for controlling liquid fuel pressure supplied to a supercharged internal combustion engine fuel injector or injectors, comprising housing structure having fuel inlet and outlet ports, and a first chamber through which fuel flows in flowing to and through the ports, and through a valving port in the chamber; the housing structure also defining a second chamber spaced from the first chamber; a diaphragm assembly extending between the chambers and movable relative thereto, the assembly including a first diaphragm having a first side exposed to the first chamber, and a second diaphragm having a first side exposed to the second chamber; structure for communicating engine manifold pressure to the second diaphragm, whereby a decrease in the manifold pressure results in a reduced liquid fuel pressure delivered to the injector or injectors; and a control structure associated with the assembly to allow adjustment of the effective cross sectional area of the second diaphragm.