Diaphragm means for driving a secondary throttle valve in a two-barrel carburetor

In a two-barrel carburetor having primary and secondary bores and primary and secondary throttle valves mounted therein, said second throttle valve being openable when said primary throttle valve is opened beyond a critical opening, a diaphragm means which acts in response to venturi vacuum and which controls the position of the secondary throttle valve over its entire range of movement, means for controlling the opening of the second throttle valve comprising a casing, a diaphragm which co-operates with said casing to define a diaphragm chamber on one side thereof, said diaphragm chamber being supplied with venturi vacuum, a diaphragm rod having one end connected to said diaphragm and the other end drivingly connected to said secondary throttle valve, said diaphragm rod comprises a cylinder tube having one end integrally connected with said diaphragm, a piston slidably received in said cylinder tube, and a piston one end of which is connected to said piston and the other end of which projectss outward from the other end of said cylinder tube which is connected to the secondary throttle valve and a diaphragm spring which resiliently drives said diaphragm rod in the direction to close said secondary throttle valve, wherein said diaphragm rod is variable in length and has a biasing spring which biases the length of said rod so as to alter it in the direction to open said secondary throttle valve and a damping means which damps the biasing action of said biasing spring.