Deceleration Valve
Valve assembly is connected to inlet manifold by a nut and tapered adaptor. Valve body contains a spring loaded diaphragm which is held in place by the bottom cover. Diaphragm is subjected to manifold vacuum on top side and atmospheric pressure on the underside by a bleed hole in the cover. During deceleration manifold vacuum is sufficient for the diaphragm to overcome the spring loading and lift deceleration valve off its seat. A pipe connects chamber under deceleration valve to deceleration section of carburetor. Deceleration valve requires no routine maintenance, but failure of diaphragm will allow air to pass from bleed hole in cover through diaphragm and straight into inlet manifold. Resulting weak mixture may give rise to persistent stalling and irregular idling. If condition present and carburetor and ignition settings are correct, check diaphragm by covering bleed hole. If idling is restored, replace deceleration valve diaphragm.