and wall 25 of body 26 is a coil spring 24 which urges piston 24 outward to contact cap 29 a valve assembly is located in the opposite end of body 26 and throttles the vacuum level within the interior chamber 30 of motor 1 as set forth below piston 28 moves within body 26 in response to vacuum level in chamber 30 the valve assembly includes a valve 10 that moves up and down in a vertical direction to control throttle the flow between chambers 20 amp 21 and chamber 30 by way of bore 30a chamber 20 is connected by way of the previously described line 50 to intake manifold 27 and located at the lower end of valve 10 is a flexible diaphragm 18 which responds to the pressure gradient between chamber 20 and the ambient through vent 36 to move valve 10 in the vertical direction at the opposite end of valve 10 is a calibrated control spring 12 which urges valve 10 in the vertical direction opposing diaphragm 18 a seat 13 is provided for spring 12 on the top of valve 10 and spring 12 is held in place by a split ring washer 15 that is radially contracted to fit within the adjacent slot in body 26 as shown a spacing washer 5 is disposed between washer 15 and spring 12 for proper tensioning of spring 12 valve 10 moves in the vertical direction in response to the vacuum level applied to inlet 20 from manifold 27 and as the vacuum level in inlet 20 increases the pressure gradient across diaphragm 18 also increases whereby.