Some major parts of a Roosa Master fuel injection pump are the rotor, metering valve, several passages, transfer pump and the plunger. A fuel injection pump typically has more than 100 components and only four rotating members, with no ball-bearings, gears or spring-loaded components.
The Roosa Master is a single-cylinder pump that uses metering to control the gas/air ratio that enters the cylinders. Two opposed plungers, initiated by a cam ring, pump fuel through the single chamber to a multi-cylinder engine. The transfer pump has a pressure-regulating system that allows it to distribute fuel to multiple passages. The amount of rotation of the rotor changes the position of the metering valve that controls the amount of fuel to the plunger.