GM Chevy Mid-Size Cars 1964-1988 Repair Guide

Rochester MV 1-BBL Carburetor

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See Figure 1

The model MV carburetor is a single bore, downdraft carburetor with an aluminum throttle body, automatic choke, internally balanced venting, and a hot idle compensating system for cars equipped with automatic transmissions. Newer models are also equipped with Combination Emission Control valves (C.E.C.) and an Exhaust Gas Recirculation (EGR) system. An electrically operated idle stop solenoid replaces the idle stop screw of older models. The MV carburetor is used on six cylinder cars from 1968 and service procedures apply to all MV carburetors.



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Fig. Fig. 1: Exploded view of the Rochester MV carburetor

FAST IDLE ADJUSTMENT



The fast idle adjustment must be made with the transmission in Neutral.

  1. Position the fast idle lever on the high step of the fast idle cam.
  2.  
  3. Be sure that the choke is properly adjusted and in the wide open position with the engine warm.
  4.  
  5. Bend the fast idle lever until the specified speed is obtained.
  6.  

CHOKE ROD (FAST IDLE CAM) ADJUSTMENT



See Figure 2

Adjust the fast idle before making choke rod adjustments.

  1. Place the fast idle cam follower on the second step of the fast idle cam and hold it firmly against the rise to the high step.
  2.  
  3. Rotate the choke valve in the direction of the closed choke by applying force to the choke coil lever.
  4.  
  5. Bend the choke rod, at the partial elbow that exists partway up the rod from the thermostatic coil, in order to give the specified opening between the lower edge (upper edge-1976), of the choke valve and the inside air horn wall.
  6.  

Measurement must be made at the center of the choke valve.



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Fig. Fig. 2: Adjusting the choke rod-Rochester MV

CHOKE VACUUM BREAK ADJUSTMENT



See Figure 3

The adjustment of the vacuum break diaphragm unit ensures correct choke valve opening after engine starting.

  1. Remove the air cleaner assembly for access. On vehicles with the THERMAC air cleaner, plug the sensor's vacuum take off port.
  2.  
  3. Using an external vacuum source, apply vacuum to the vacuum break diaphragm until the plunger is fully seated.
  4.  
  5. When the plunger is seated, push the choke valve toward the closed position.
  6.  



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Fig. Fig. 3: Choke vacuum break adjustment-Rochester MV

CHOKE UNLOADER ADJUSTMENT



  1. While holding the choke valve closed, apply pressure to the choke operating lever.
  2.  
  3. Turn the throttle lever to the wide open position.
  4.  
  5. Measure the distance between the lower edge of the choke plate and the air horn wall.
  6.  
  7. If an adjustment is necessary, carefully bend the unloader tang on the throttle lever.
  8.  

FLOAT LEVEL ADJUSTMENT



See Figure 4

  1. While holding the float retainer in place, push down on the outer end of the float arm.
  2.  
  3. Measure the distance from the top of the float bowl casting (no gasket) and the toe of the float.
  4.  
  5. Bend the float as necessary to obtain the specified measurement.
  6.  



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Fig. Fig. 4: Adjusting the float level on a Rochester MV

METERING ROD ADJUSTMENT



  1. Back out the idle adjusting screw or idle stop solenoid to close the throttle valve.
  2.  
  3. Apply pressure to the power piston hanger and hold the piston against its stop.
  4.  
  5. While holding the power piston down, turn the metering rod holder over the float surface of the bowl casting until the metering rod lightly touches the inside edge of the bowl.
  6.  
  7. Measure the space between the bowl and the bottom of the metering rod holder. This dimension should be 0.070-0.078 in. (1.778-1.981mm).
  8.  
  9. Bend the metering rod holder if an adjustment is necessary.
  10.  

CHOKE ROD ADJUSTMENT



  1. Disconnect the choke rod from the upper choke lever and hold the choke valve closed.
  2.  
  3. Push the choke rod down to the bottom of its travel.
  4.  
  5. The top of the rod should be even with the bottom of the hole in the choke lever, carefully bend the rod if adjustment is necessary.
  6.  

 
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