a plurality of valves, each valve being positioned adjacent a respective one of the dilution ports for controlling the flow of air through the dilution ports, each valve being settable to maintain one of a plurality of different open configurations, each valve being arranged for reciprocating movement and said combustor further comprising control means for variably controlling the setting of the valves wherein the control means comprises a rotatable actuating ring, the actuating ring has a plurality of camming surfaces and each valve has a cam follower arranged to rest on a respective one of the plurality of camming surfaces.