ROCHESTER CARBURETORS

Bulletin 9C-303 1 April 1953

CHEVROLET-1953 SYNCROMESH - Auto. Choke Curb. 7004915
CARBURETOR ADJUSTMENTS
Make adjustments in following order—
FLOAT LEVEL ADJUSTMENT
With air horn fully assembled, gasket in position and assembly up-ended on a flat surface (Figure 1):
1.  Place float level gauge in position with gauge tang inserted in discharge nozzle.
2.  Bend float arms vertically so that each float just touches top portion of gauge.
3.  Bend float arms horizontally so that each float is centered in gauge.
4.  Tilt assembly 90° each side and check that floats do not touch gauge.
FLOAT DROP ADJUSTMENT
As shown in Figure 2, to insure sufficient entry of fuel under high speed operation, it is necessary to check and adjust the float drop. With air horn held right side up and floats suspended freely, carefully bend the float tang at the rear of the float assembly so that the bottom of the float is 1-3/4" below the gasket surface. Install air horn assembly to float bowl and tighten screws evenly and securely.
CHOKE ROD ADJUSTMENT
1.  With the stat cover properly indexed (so that the scribed index mark on the cover is in line with the long cast mark on the choke housing) turn the idle screw in until it contacts the second step of the fast idle cam against the shoulder of the highest step. (Figure 3.)
2.  Holding the screw tightly against the cam, bend the choke rod at the dog leg until the small end of combination gauge (.073") just slides easily be­tween the lower edge of the choke valve and the bore of the carburetor air horn.
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FIGURE 1
FIGURE 2
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FIGURE 3
FIGURE 4
UNLOADER ADJUSTMENT
With the throttle lever in the full wide open position, there should be a clearance between the lower edge of the choke valve and the bore of the carburetor air horn so that the large end of the combination gauge (.166") will just slide freely (Figure 4). Bend the tang on the throttle lever to obtain the necessary clearance.
NOTE: No other carburetor adjustments are required.
          Bending tool BT-18, float level gauge M-250, and combination carburetor gauge BT-64 are available from
                                            Borroughs Tool Company, Kalamazoo, Mich., U.S.A.
 
 
AUTOMATIC CHOKE STOVE ADAPTER KIT INSTALLATION
1.  Assemble carburetor to engine manifold. Connect the car­buretor controls, gasoline and vacuum spark control lines.
2.  Mount manifold stove assembly on exhaust manifold be­tween No. 1 and No. 2 exhaust ports so that hot air tube connection is offset slightly towards the rear of the engine (Figure 5). Do not tighten retainer screw securely until tube installation is made.
3. Place tapered end of hot air tube, into manifold stove con­nection. Then by ad­justing the position of the manifold stove on the exhaust mani­fold, assemble the tube fitting to the carburetor choke housing connection until it is finger tight.
4. After this assem­bly has been made, tighten the stove re­tainer screw and tube fitting  securely.
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TUNE-UP SPECIFICATIONS
Spark Plug Gap                    Breaker Point Gap
.035"
.016".021" New Installation .013".018" Old Points
Ignition Timing
Idling RPM
5° BTDC
475 in "N"
CARBURETOR SPECIFICATIONS
Dimensions: Primary Venturi—1-11/32" Secondary Venturi—19/32"
Identification: Main Metering Jet—Stamped 58 (Square
Approach) Air Horn Gasket—Stamped 4480                 
Idle Discharge Holes: Idle Needle Orifice—.073" Second idle Hole—.040" x .010" Nick Third Idle Hole—.028" x .065" Above Spark Drilling—Slot .175" x .045;
Top Loc. .029" Above Valve
Pump Discharge Hole—.031" Choke Restriction—.089"               
Power Restriction—.039"

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