Carburettors for internal combustion engines

A carburettor for an internal combustion engine comprising a body, an air passageway therethrough, leading in use from ambient air to the internal combustion engine and including a venturi tube therein, a movable air control valve member in or adjacent said venturi tube and forming part of a movable assembly, a fuel control valve member associated with said air control valve member, a movable wall connected to but spaced away from said air control valve member so as to be movable therewith and so as to form part of said movable assembly, said movable wall separating a first and second pressure chamber in said body, biasing means to bias said movable assembly to a biased position, a low pressure conduit between a part of said first pressure chamber, a pressure control entry to said first pressure chamber, a balancing pressure entry to said second pressure chamber, a low pressure control valve member controlling pressure from said low pressure conduit to said air passageway in which engine vacuum exists to use and said first pressure chamber and positionable relative to a part movable with said movable assembly and manually operable actuating means to programme positioning of said low pressure control valve member so that movement of said movable assembly relative to said low pressure control valve member due to relative forces acting on said movable assembly causes variation of pressures in said first pressure chamber and hence variation of position of said movable assembly including said air control valve member and said fuel control valve member to control power from an internal combustion engine to which the carburettor is fixed in accordance with selected positions of said manually operable actuating means.