1942 - 1947 Chevrolet Shop Manual



	6-44

	5. Assemble vacuum power jet push rod in jet. Assemble accelerating pump sleeve in end of pump cylinder with the holes in the sleeve down. When the carburetor throttle valve is removed, care must be taken when reassembling to make sure the notch machined in the valve lines up with the port for the vacuum spark advance. 6. Assemble the spring, piston and plug in the vacuum power cylinder in the order shown in Fig. 92. Then install the idle passage tube and idle adjusting screw in the carburetor upper body.	8. Install gaskets on carburetor body and assemble the upper carburetor body to the lower. During this operation care should be used to properly enter the accelerating pump piston and the vacuum power jet push rod. Install and tighten the carburetor body screws. Assemble the choke link, washer and hairpin. When installing the carburetor on the truck the special gaskets, shown in Fig. 94, must be installed between the carburetor and the riser, otherwise the port for the vacuum power cylinder will be covered and high gasoline consumption will result.


		Fig. 94—Vacuum Power Cylinder Port To adjust the carburetor idle set the throttle stop screw so the engine runs at 450 to 500 R.P.M. Then set the idle adjustment screw so the engine fires evenly. Correct setting will be found between 1/2 to 1-1/4 turns open. FUEL PUMP The fuel pump, Fig. 95, is of the diaphragm type. It is attached to the Crankcase and operated by an eccentric on the camshaft. The diaphragm is composed of several layers of specially treated cloth which is not affected by gasoline or benzol. The cloth material is held between two metal discs and is pushed upward by a pump spring, and downward by an arm operated by the eccentric on the camshaft. The diaphragm. in its downward movement causes a vacuum in the pump chamber and gasoline is drawn in through the glass bowl and strainer to fill this vacuum. The upward movement of the diaphragm forces gasoline to the carburetor. The repeated movement of the diaphragm is possible, indefinitely, without injury, due to the extreme flexibility of the material of which it is made. Further, movement of the diaphragm occurs only when the carburetor requires gasoline. When this occurs, the movement of the diaphragm is in
	Fig. 92—Vacuum Spring, Piston and Plug Assembly 7. Assemble fibre washer, piston, spring and spring retainer on the accelerating pump rod and plate assembly. Then compress the spring and connect the rod to the link by installing the brass pin, Fig. 93.

	Fig. 93—Accelerating Pump