Engine intake system with deceleration valve

An engine intake system, including a carburetor having an air/fuel induction passage connected to air at one end and the engine intake manifold at the other end, a throttle valve rotatably mounted in the passage for blocking or admitting flow therethrough, an air bleed air bypass passage connected from the one end of the induction passage to the other bypassing the throttle valve to admit air to the manifold when the throttle valve is in a closed engine idle speed position to decay the manifold vacuum therein during engine decelerating conditions, a deceleration valve in the air bypass passage having a valve member operative to open and close the bypass passage, servo means to move the deceleration valve in response to changes in engine operating conditions including a housing divided by a flexible diaphragm into first and second pressure chambers each having an inlet connected to manifold vacuum, and an auxiliary control valve connected in the inlet to said second chamber and adapted to admit vacuum when the engine is idling, and to trap idle vacuum in the chamber when the engine is not idling, the valve member being connected to the diaphragm so that movement of the diaphragm opens and closes the deceleration valve, said auxiliary control valve being controllable by spark port pressure in a port in the induction passage located just upstream of the closed position of the throttle valve so as to change from atmospheric pressure to manifold vacuum as the throttle valve moves open to control a supply of manifold vacuum at various pressure levels to both the first and second chambers to effect movement of the deceleration valve, the auxiliary valve being movable from a first position at low spark port vacuum levels to connect manifold vacuum to the second chamber to maintain the deceleration valve closed, to a second position at higher spark port vacuum levels connecting higher deceleration level manifold vacuum to the first chamber to open the deceleration valve and bleed the vacuum in the manifold.