A fuel system includes an air and fuel mixer configured to mix air and fuel provided to a combustion engine and a fuel path coupled to the air and fuel mixer. The fuel path includes an electronically controlled fuel control valve configured to regulate an air to fuel ratio of an air/fuel mixture provided to the engine, a gas pressure regulator disposed upstream of the fuel control valve and configured to control a pressure of the fuel in relation to an air pressure of the air and fuel mixer, and a manual adjust valve disposed downstream of the gas pressure regulator and configured to mechanically tune a performance of the fuel path to minimize an adjustment by the electronically controlled fuel control valve to regulate the air to fuel ratio. The fuel system is configured to operate with different fuels that differ in physical and chemical properties.