Abstract: A rotor housing assembly is adapted such that a barrel valve is arranged to regulate the flow of fuel/air mixture both from outside the housing assembly into an internal lubrication flow path and from the internal lubrication flow path into an internal chamber. The barrel valve includes a substantially cylindrical valve member diagonally traversed by a separation plate, dividing the interior of the valve member into an inlet chamber and an outlet chamber. Fuel/air mixture entering the housing assembly from outside passes through the inlet chamber and fuel/air mixture entering the internal chamber passes through the outlet chamber.