|Carter WD0, 2 Barrel Carburetor Starter Switch|
The Carter WD0 starter switch is incorporated in the 1939 Dual Carburetor as used on Buick. There is a milled groove on the throttle shaft into which rests a steel forced against the brass plunger "B" which moves bakelite guide "C:" and a contact spring "E", shaped like the letter W, up until it makes an electrical contact between two brass inserts molded in the bakelite terminal cap "H" on the switch and starts the motor. The manifold vacuum acts upon the steel ball and as soon as the foot throttle is released the ball is drawn up by suction away from the shaft, spring returns and breaks contact, and the ball remains in the upper position as long as the motor is in operation. Any future operation of the throttle does not make switch contact until motor stops.
The W shaped contact spring "E" rests on two or more brass shims "D" with square holes. These are very important because they determine the point at which the switch contact is made. Contact should be made when throttle valve is opened between 30 and 40 degrees. If not enough of these shims are in place contact will not be made soon enough. If there are too many of these the switch will begin to function too soon before 30 degrees and in that case there is danger that the switch may be in contact all the time.
When disassembling the switch be careful not to lose the shims as they are not available and they need to be returned to their same position.