Chevrolet Full-size Cars 1968-1978 Repair Guide

Rochester MV 1-Bbl. Carburetor

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Fig. Fig. 1 MV Carburetor Specifications



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Fig. Fig. 2 Exploded view of the Rochester MV carburetor

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 vehicles equipped with automatic transmission. Newer models are also equipped with Combination Emission Control valves (CEC) and an Exhaust Gas Recirculation (EGR) system. An electrically operated idle stop solenoid replaced the idle stop screw of older models.

The MV carburetor is used on six cylinder vehicles from 1968 and service procedures apply to all MV carburetors.

ADJUSTMENTS



Fast Idle

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)

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 point shown in the illustration, 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.

Choke Vacuum Break


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Fig. Fig. 3 Vacuum break adjustment for the Rochester MV carburetor

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

  1. Remove the air cleaner. 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.  

Choke Unloader
  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, bend the unloader tang on the throttle lever.
  8.  

Float Level


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Fig. Fig. 4 Adjusting the float level on the Rochester MV carburetor

  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.  

Metering Rod
  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".
  8.  
  9. Bend the metering rod holder if an adjustment is necessary.
  10.  

Choke Rod


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Fig. Fig. 5 Adjusting the choke rod on the Rochester MV carburetor

  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, band the rod if necessary.
  6.  

 
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