ROCHESTER CARBURETORS

Bulletin 9C-330 15 December 1957

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Rochester Carburetors MODEL 4GC
1957-58 CHEVROLET "V-8" POWER PACK ADJUSTMENTS AND SPECIFICATIONS
BULLETIN 9C-330
PAGE 3 OF 4 DATE: 12/15/57
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SETTING 1-1/16", GAUGE BT-145 OR SCALE
Back out idle screw until throttle valves are completely closed. Place combination "pump" and "vent" gauge on top of air next to pump plunger, as shown. With the throttle valves closed and lower edge of gauge resting on top of air horn, the pump plunger shaft should slide freely into hole of gauge marked "pump"
Bend the pump rod with Bending Tool BT-18 as shown to adjust.
1957 SETTING 1-5/8" (PRIM. and SEC), GAUGE BT-89
1958 SETTING 1-5/8" (PRIMARY), GAUGE BT-89 SETTING 1-11/16" (SECONDARY), GAUGE BT-143
With the air horn gasket in place, position the gauge over the floats and against the curvature in the air horn bore. Bend the float arms at the rear of the assembly so floats just touch the gauge. Then bend float arms horizontally to center each pontoon between the gauge legs.
Note: 1958 secondary float setting differs from primary. Use gauges and dimensions listed above.
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SETTING 31/32", GAUGE BT-145 OR SCALE Note: Make pump rod adjustment before adjusting idle vent
valve.
Place combination "pump" and "vent" gauge on top of air
horn with side marked "vent" next to pump plunger shaft,
as shown.
Open throttle valves to point where the vent valve is just closed. With the throttle valves held in this position, the hole marked "vent" on the gauge should slide freely over pump plunger shaft.
Bend the tang on the pump lever, as shown to adjust.
SETTING 2-1/4", GAUGE BT-93 OR SCALE
Bend the float tang as required to obtain a distance of 2-1/4" from the gasket surface to the bottom of the float, with the float hanging free.
1957 SETTING, 1 NOTCH LEAN
1958 SETTING, 1 NOTCH LEAN (POWERGLIDE),
INDEX (TURBOGLIDE)
Loosen the three retaining screws and rotate the choke cover counterclockwise against coil tension until the index mark is in the proper position with the index point on the choke housing.
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SET MARK ON COVER TO SPECIFIED POINT ON CHOKE HOUSING
FORM NO. 1258 l.P.S. PRINTED IN U.S.A..

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