Abstract: An integrated fuel control unit for gas-operated internal combustion engines that includes a base on which a primary diaphragm is secured to define a primary fuel chamber. A primary fuel orifice is carried by the base, as is a primary control lever that is coupled to the primary diaphragm for controlling flow of fuel through the primary orifice as a function of inlet fuel pressure and engine demand. A secondary diaphragm is also secured to the base to define a secondary fuel chamber. A secondary orifice is carried by the base between the primary and secondary chambers, and a secondary control lever is coupled to the secondary diaphragm for controlling flow of fuel through the secondary orifice as a function of engine demand. A heat exchange section in the body receives engine coolant or engine oil for heat exchange with fuel so as to heat and vaporize the fuel between the primary and secondary chambers.