GM Camaro 1967-1981 Repair Guide

Carburetors

Print

Since its introduction in 1967, the Camaro has used thirteen different carburetors:



Carter YF 1 bbl-1967
 
Rochester BV 1 bbl-1967
 
Rochester MV 1 bbl-1968-76
 
Rochester 2GV 2 bbl-1968-76
 
Rochester 4MV 4 bbl-1968-74
 
Holley 4150 4 bbl-1969-72
 
Rochester 1ME 1 bbl-1977-79
 
Rochester 2GC 2 bbl--1975-79
 
Rochester M4MC 4 bbl-1975-79
 
Rochester M2ME 2 bbl-1980
 
Rochester M4ME 4 bbl-1980
 
Rochester E2ME 2 bbl-1980-81
 
Rochester E4ME 4 bbl-1980-81
 

MODEL IDENTIFICATION



General Motors Rochester carburetors are identified by their model code. The first number indicates the number of barrels, while one of the last letters indicates the type of choke used. These are V for the manifold mounted choke coil, C for the choke coil mounted in the carburetor body, and E for electric choke, also mounted on the carburetor. Model codes ending in A indicate an altitude-compensating carburetor.

See Figures 1 through 9



Click image to see an enlarged view

Fig. Fig. 1: Disconnect the fuel line-always use flare nut wrenches, to prevent the fitting from rounding off ...



Click image to see an enlarged view

Fig. Fig. 2: ... and use a backup wrench, to prevent damage to the second fitting (mounted in the carburetor)



Click image to see an enlarged view

Fig. Fig. 3: Label or mark the vacuum hoses for reinstallation and detach them from the carburetor



Click image to see an enlarged view

Fig. Fig. 4: Disconnect the power brake booster vacuum line (if equipped) from the carburetor base



Click image to see an enlarged view

Fig. Fig. 5: Remove the accelerator cable retaining clip and slide the cable off the lever stud ...



Click image to see an enlarged view

Fig. Fig. 6: ... remove the throttle return spring(s) ...



Click image to see an enlarged view

Fig. Fig. 7: ... and remove the transmission kickdown cable from the lever-these three steps can be done in any order



Click image to see an enlarged view

Fig. Fig. 8: Remove the four mounting nuts or bolts ...



Click image to see an enlarged view

Fig. Fig. 9: ... then lift the carburetor off the intake manifold-remove the old gasket prior to installation

REMOVAL & INSTALLATION



All Carburetors
  1. Remove the air cleaner and its gasket.
  2.  
  3. Disconnect the fuel and vacuum lines from the carburetor.
  4.  
  5. Disconnect the choke coil rod, heated air line tube, or electrical connector.
  6.  
  7. Disconnect the throttle linkage.
  8.  
  9. On automatic transmission cars, disconnect the throttle valve linkage, if so equipped.
  10.  
  11. If CEC equipped, remove the CEC valve vacuum hose and electrical connector. Disconnect the EGR line, if so equipped.
  12.  
  13. Remove the idle stop solenoid, if so equipped.
  14.  
  15. Remove the carburetor attaching nuts and/or bolts, gasket or insulator, and remove the carburetor.
  16.  
  17. Install the carburetor using the reverse of the removal procedure. Use a new gasket and fill the float bowl with gasoline to ease starting the engine.
  18.  

OVERHAUL



All Types

See Figures 10 through 15

Click image to see an enlarged view

Fig. Fig. 10: Exploded view of an early Rochester® MV Monojet carburetor-not equipped with CEC components or an idle stop solenoid



Click image to see an enlarged view

Fig. Fig. 11: Exploded view of a late Rochester® MV Monojet carburetor-=uipped with CEC components and an idle stop solenoid



Click image to see an enlarged view

Fig. Fig. 12: Exploded view of typical Rochester® 2G, 2GC and 2GV carburetors



Click image to see an enlarged view

Fig. Fig. 13: Exploded view of a Rochester® 4MC Quadrajet carburetor



Click image to see an enlarged view

Fig. Fig. 14: Exploded view of a typical Holley® 4150 carburetor



Click image to see an enlarged view

Fig. Fig. 15: Holley® 4150 carburetor exploded view key list

Efficient carburetion depends greatly on careful cleaning and inspection during overhaul, since dirt, gum, water, or varnish in or on the carburetor parts are often responsible for poor performance.

Overhaul your carburetor in a clean, dust-free area. Carefully disassemble the carburetor, referring often to the exploded views and directions packaged with the rebuilding kit. Keep all similar and look-alike parts segregated during disassembly and cleaning to avoid accidental interchange during assembly. Make a note of all jet sizes.

When the carburetor is disassembled, wash all parts (except diaphragms, electric choke units, pump plunger, and any other plastic, leather, fiber, or rubber parts) in clean carburetor solvent. Do not leave parts in the solvent any longer than is necessary to sufficiently loosen the deposits. Excessive cleaning may remove the special finish from the float bowl and choke valve bodies, leaving these parts unfit for service. Rinse all parts in clean solvent and blow them dry with compressed air or allow them to air dry. Wipe clean all cork, plastic, leather, and fiber parts with a clean, lint-free cloth.

Blow out all passages and jets with compressed air and be sure that there are no restrictions or blockages. Never use wire or similar tools to clean jets, fuel passages, or air bleeds. Clean all jets and valves separately to avoid accidental interchange.

Check all parts for wear or damage. If wear or damage is found, replace the defective parts. Especially check the following:

  1. Check the float needle and seat for wear. If wear is found, replace the complete assembly.
  2.  
  3. Check the float hinge pin for wear and the float(s) for dents or distortion. Replace the float if fuel has leaked into it.
  4.  
  5. Check the throttle and choke shaft bores for wear or an out-of-round condition. Damage or wear to the throttle arm, shaft, or shaft bore will often require replacement of the throttle body. These parts require a close tolerance of fit; wear may allow air leakage, which could affect starting and idling.
  6.  

Throttle shafts and bushings are not included in overhaul kits. They can be purchased separately.

  1. Inspect the idle mixture adjusting needles for burrs or grooves. Any such condition requires replacement of the needle, since you will not be able to obtain a satisfactory idle.
  2.  
  3. Test the accelerator pump check valves. They should pass air one way but not the other. Test for proper seating by blowing and sucking on the valve. Replace the valve check ball and spring as necessary. If the valve is satisfactory, wash the valve parts again to remove breath moisture.
  4.  
  5. Check the bowl cover for warped surfaces with a straightedge.
  6.  
  7. Closely inspect the accelerator pump plunger wear and damage, replacing as necessary.
  8.  
  9. After the carburetor is assembled, check the choke valve for freedom of operation.
  10.  

Carburetor overhaul kits are recommended for each overhaul. These kits contain all gaskets and new parts to replace those which deteriorate most rapidly. Failure to replace all parts supplied with the kit (especially gaskets) can result in poor performance later.

Some carburetor manufacturers supply overhaul kits of three basic types: minor repair; major repair; and gasket kits. Basically, they contain the following:

Minor Repair Kits:


All gaskets
 
Float needle valve
 
All diagrams
 
Spring for the pump diaphragm
 

Major Repair Kits:


All jets and gaskets
 
All diaphragms
 
Float needle valve
 
Pump ball valve
 
Float
 
Complete intermediate rod
 
Intermediate pump lever
 
Some cover hold-down screws and washers
 

Gasket Kits:


All gaskets
 

After cleaning and checking all components, reassemble the carburetor, using new parts and referring to the exploded view. When reassembling, make sure that all screws and jets are tight in their seats, but do not overtighten as the tips will be distorted. Tighten all screws gradually, in rotation. Do not tighten needle valves into their seats; uneven jetting will result. Always use new gaskets. Be sure to adjust the float level when reassembling.

PRELIMINARY CHECKS (ALL CARBURETORS)



The following should be observed before attempting any adjustments.

  1. Thoroughly warm the engine. If the engine is cold, be sure that it reaches operating temperature.
  2.  
  3. Check the torque of all carburetor mounting nuts and assembly screws. Also check the intake manifold-to-cylinder head bolts. If air is leaking at any of these points, any attempts at adjustment will inevitably lead to frustration.
  4.  
  5. Check the manifold heat control valve (if used) to be sure that it is free.
  6.  
  7. Check and adjust the choke as necessary.
  8.  
  9. Adjust the idle speed and mixture. If the mixture screws are capped, don't adjust them unless all other causes of rough idle have been eliminated. If any adjustments are performed that might possibly change the idle speed or mixture, adjust the idle and mixture again when you are finished.
  10.  

Before you make any carburetor adjustments make sure that the engine is in tune. Many problems which are thought to be carburetor-related can be traced to an engine which is simply out-of-tune. Any trouble in these areas will have symptoms like those of carburetor problems.

ADJUSTMENTS



Carter YF-1 BBl Carburetor
AUTOMATIC CHOKE
  1. Disconnect the choke rod from the choke lever.
  2.  
  3. Hold the choke valve closed and pull the rod up against the stop in the thermostat housing.
  4.  
  5. The top of the rod should be about one rod diameter above the top of the hole in the choke lever. If not, adjust the length of the rod by bending it at the bend.
  6.  
  7. Connect the choke rod at the lever.
  8.  

HAND CHOKE
  1. Push in the hand choke knob until the knob is within 1 / 8 in. of the dash.
  2.  
  3. Loosen the cable clamp at the carburetor and adjust the cable until the choke is wide open.
  4.  
  5. Tighten the cable clamp and check the operation of the choke.
  6.  

IDLE VENT
  1. With the choke open, back out the idle speed screw until it is free to close the throttle valve.
  2.  
  3. Insert a feeler gauge between the air horn and the vent valve. Adjust to get 0.065 in. clearance.
  4.  

FAST IDLE AND CHOKE VALVE
  1. Hold the choke valve closed.
  2.  
  3. Close the throttle and mark the position of the throttle lever tang on the fast idle cam.
  4.  
  5. The mark on the fast idle cam should align with the upper edge of the tang on the throttle lever. If not, bend the choke rod as necessary.
  6.  

CHOKE UNLOADER
  1. Open the throttle to the wide open position.
  2.  
  3. Using a rubber band, hold the choke valve closed.
  4.  
  5. Bend the unloader tang on the throttle lever to get the proper clearance (0.250 in.) between the lower edge of the choke valve and the air horn wall.
  6.  

VACUUM BREAK
  1. Hold the vacuum break arm against its stop and hold the choke closed with a rubber band.
  2.  
  3. Bend the vacuum break link to establish a clearance of 2.220 in. (automatic transmission) or 0.240 in. (standard transmission) between the lower edge of the choke valve and the air horn wall.
  4.  

FLOAT LEVEL
  1. Turn the bowl cover upside down and measure the float level by measuring the distance between the float (free end) and cover. This distance should be 7 / 32 in.; if not, bend the lip of the float, not the float arm.
  2.  
  3. Hold the cover in the proper position (not upside down) and measure the float drop from the cover to the float bottom at the end opposite the hinge. This distance should be 1 3 / 16 in.
  4.  
  5. Make any necessary adjustments with the stop tab on the float arm.
  6.  

ACCELERATOR PUMP
  1. Seat the throttle valve by backing off the idle speed screw.
  2.  
  3. Hold the throttle valve closed.
  4.  
  5. Fully depress the diaphragm shaft and check the contact between the lower retainer and the lifter link.
  6.  
  7. This retainer (upper pump spring) should just contact the pump lifter link. Do not compress the spring.
  8.  
  9. Bend the pump connector link at its "U" bend to make corrections.
  10.  

METERING ROD
  1. Insert the metering rod through the metering jet and close the throttle valve. Press down on the upper pump spring until the pump bottoms.
  2.  
  3. The metering rod arm must rest on the pump lifter link; the rod eye should just slide over the arm pin.
  4.  
  5. To adjust, bend the metering rod arm.
  6.  

Rochester BV-1 BBL Carburetor
AUTOMATIC CHOKE

See Figure 16

  1. Disconnect the choke rod from the choke lever at the carburetor.
  2.  
  3. While holding the choke valve shut, pull the choke rod up against the stop in the thermostat housing.
  4.  
  5. Adjust the length of the choke rod so that the bottom edge of the choke rod is even with the top edge of the hole in the choke lever.
  6.  
  7. Check the linkage for freedom of operation.
  8.  



Click image to see an enlarged view

Fig. Fig. 16: Idle vent adjustment-Rochester BV carburetor

IDLE VENT

See Figure 17



Click image to see an enlarged view

Fig. Fig. 17: Idle vent adjustment-Rochester® BV carburetor

  1. Position the carburetor lever on the low step of the fast idle cam.
  2.  
  3. The distance between the choke valve and the body casting should be 0.050 in.
  4.  
  5. If an adjustment is necessary, turn the valve with a screwdriver.
  6.  

FAST IDLE AND CHOKE VALVE
  1. Position the end of the idle adjusting screw on the next to highest step of the fast idle cam.
  2.  
  3. A 0.050 in. feeler gauge should slide easily between the lower edge of the choke valve and the carburetor bore.
  4.  
  5. If necessary, bend the choke rod until the correct clearance is obtained.
  6.  

UNLOADER
  1. Open the throttle to the wide open position.
  2.  
  3. A 0.230/0.270 in. gauge should slide freely between the lower edge of the choke valve and the bore of the carburetor.
  4.  
  5. If necessary, bend the throttle tang to obtain the proper clearance.
  6.  

VACUUM BREAK
  1. Hold the diaphragm lever against the diaphragm body.
  2.  
  3. The clearance between the lower edge of the choke valve and the air horn wall should be 0.136-0.154 in. on Powerglide cars and 0.154-0.173 in. on manual cars.
  4.  
  5. Bend the diaphragm link, if necessary.
  6.  

FLOAT LEVEL

See Figures 18 and 19



Click image to see an enlarged view

Fig. Fig. 18: Adjusting the float drop on Rochester® BV carburetors



Click image to see an enlarged view

Fig. Fig. 19: Rochester Bv Specifications

  1. Remove the air cleaner.
  2.  
  3. Disconnect the fuel line, fast idle rod, cam-to-choke kick lever, vacuum hose at the diaphragm, and the choke rod at the choke lever.
  4.  
  5. Remove the bowl cover screws and carefully lift the cover off the carburetor.
  6.  
  7. Install a new gasket on the cover before making any adjustments.
  8.  
  9. Invert the cover assembly and measure the float level with a float gauge.
  10.  

Rebuilding kits include a float level gauge.

  1. Check float centering while holding the cover sideways. Use the same gauge as in Step five. The floats should not touch the gauge.
  2.  
  3. Hold the cover upright and measure the float drop. If the drop is more or less than 1 3 / 4 in., bend the stop tang until the drop is correct.
  4.  
  5. Install the cover and reconnect the lines and linkage in the reverse order of removal.
  6.  

Rochester MV-1 BBL Carburetor

The model MV carburetor is a single bore, down-drift 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.

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)

See Figure 20



Click image to see an enlarged view

Fig. Fig. 20: Fast idle cam adjustment-Rochester® M and MV carburetors

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 a closed choke by applying force to the choke coil lever.
  4.  
  5. Bend the choke rod 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

See Figure 21



Click image to see an enlarged view

Fig. Fig. 21: Vacuum break adjustment (external type)-Rochester® M and MV carburetors

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

  1. Remove the air cleaner on vehicles with THERMAC air cleaner+ug the sensor's vacuum 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

See Figure 22

Click image to see an enlarged view

Fig. Fig. 22: Float level adjustment-Rochester® M and MV carburetors

  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

See Figure 23

Click image to see an enlarged view

Fig. Fig. 23: Metering rod adjustment-Rochester® M and MV carburetors

  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 to the flat 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.
  8.  
  9. Bend the metering rod holder if an adjustment is necessary.
  10.  

CHOKE ROD

See Figures 24 and 25

Click image to see an enlarged view

Fig. Fig. 24: Choke coil rod (left-hand and upper right-hand diagrams) and CEC valve (lower right-hand diagram) adjustments-Rochester® M and MV carburetors



Click image to see an enlarged view

Fig. Fig. 25: Rochester MV Specifications

  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; bend the rod if necessary.
  6.  

Rochester 1ME-1 BBL Carburetors
FLOAT LEVEL
  1. Push down on the end of the float arm and against the top of the float needle to hold the retaining pin firmly in place.
  2.  
  3. While holding the position of the retaining pin, gauge from the top of the casting to the top of the index point at the toe of the float.
  4.  
  5. If float level needs to be changed do it by bending the float arm just on the float side of the float needle.
  6.  

FAST IDLE

See Figure 26

Click image to see an enlarged view

Fig. Fig. 26: Fast idle adjustment-Rochester® ME carburetor

Perform the adjustment with engine hot and choke open.

  1. If the carburetor has a stepped fast idle cam, put the cam follower on the high step of the cam. If the cam has a smooth contour, open the throttle slightly and rotate the cam to its highest position, then release throttle.
  2.  
  3. Support the lever with a pair of pliers, and bend the tang in or out to achieve specified rpm.
  4.  

CHOKE COIL LEVER

See Figure 27

Click image to see an enlarged view

Fig. Fig. 27: Choke coil lever adjustment-Rochester® ME carburetor

This adjustment requires a plug gauge or other metal rod of .120 in. diameter.

  1. Place the fast idle cam follower on the highest step of the cam or rotate the cam to its highest possible position. Close the choke all the way and hold.
  2.  
  3. Insert the plug gauge through the small hole in the outer end of the choke lever. Bend the link at the lowest point of the curved portion until the gauge will enter the hole in the carburetor casting.
  4.  

CHOKE

See Figure 28

Click image to see an enlarged view

Fig. Fig. 28: Electric choke setting-Rochester® ME carburetor



Click image to see an enlarged view

Fig. Fig. 29: Rochester ME Specifications

  1. Place the fast idle cam follower on the high step of the cam or rotate the cam until it is at the highest position.
  2.  
  3. Slightly loosen the three screws, which retain the choke cover, just enough to turn the cover-don't loosen them more than necessary, or the lever may slip out of the tang inside.
  4.  
  5. Turn the cover until the mark on the cover lines up with the appropriate mark on the choke housing-see specifications.
  6.  

METERING ROD
  1. Hold the throttle wide open. Push downward on the metering rod until it can be slid out of the slot in the holder. Slide the rod out of the holder and remove it from the main metering jet.
  2.  
  3. Back out solenoid hex screw until the throttle can be closed all the way.
  4.  
  5. Remove float bowl gasket.
  6.  
  7. Holding power piston down and throttle closed, swing the metering rod holder over the flat surface of the bowl casting next to the throttle bore. Measure the distance from the flat surface to the outer end of the rod holder with the specified gauge (see specifications), or a metal rod of equivalent diameter.
  8.  
  9. Bend the horizontal portion of the rod holder (where it joins the vertical portion) until the gauge just passes between the holder and surface of the bowl casting with the power piston bottomed.
  10.  

Rochester 2GC, 2GV-2 BBL Carburetors

These procedures are for both the 1 1 / 4 and 1 1 / 2 models; where there are differences these are noted. The 1 1 / 2 model has larger throttle bores and an additional fuel feed circuit to make it suitable for use on the 350 V8's.

FAST IDLE

On 2GC and 2GV models the fast idle is set automatically when the curb idle and mixture is set.

FAST IDLE CAM

See Figure 30

Click image to see an enlarged view

Fig. Fig. 30: Fast idle cam adjustment-Rochester® 2GC and 2GV carburetors

  1. Turn the idle screw onto the second step of the fast idle cam, abutting against the top step.
  2.  
  3. Hold the choke valve toward the closed position and check the clearance between the upper edge of the choke valve and the air horn wall.
  4.  
  5. If this measurement varies from specifications, bend the tang on the choke lever.
  6.  

CHOKE UNLOADER

See Figure 31

Click image to see an enlarged view

Fig. Fig. 31: Choke unloader adjustment-Rochester® 2GC and 2GV carburetors

  1. Hold the throttle valves wide open and use a rubber band to hold the choke valve toward the closed position.
  2.  
  3. Measure the distance between the upper edge of the choke valve and the air horn wall.
  4.  
  5. If this measurement is not within specifications, bend the unloader tang on the throttle lever to correct it.
  6.  

ACCELERATOR PUMP ROD

See Figure 32

Click image to see an enlarged view

Fig. Fig. 32: Accelerator pump rod adjustment-Rochester® 2GV carburetor

  1. Back out the idle stop screw and close the throttle valves in their bores.
  2.  
  3. Measure the distance from the top of the air horn to the top of the pump rod.
  4.  
  5. Bend the pump rod at the proper angle to correct this dimension.
  6.  

FLOAT LEVEL

See Figure 33

Click image to see an enlarged view

Fig. Fig. 33: Float level adjustments-Rochester® 2GC and 2GV carburetors

Invert the air horn and, with the gasket in place and the needle seated, measure the level as follows:

On nitrophyl (black plastic) floats, measure from the air horn gasket to the lip on the toe of the float.

On brass floats, measure from the air horn gasket to the lower edge of the float seam.

Bend the float tang to adjust the level.

FLOAT DROP

See Figures 34 through 39

Click image to see an enlarged view

Fig. Fig. 34: Float drop adjustment-Rochester® 2GC and 2GV carburetors with plastic floats



Click image to see an enlarged view

Fig. Fig. 35: Float drop adjustment-Rochester® 2GC and 2GV carburetors with metal floats



Click image to see an enlarged view

Fig. Fig. 36: Rochester 2GC, 2GV Specifications



Click image to see an enlarged view

Fig. Fig. 37: Rochester 2GC, 2GV Specifications (Cont.



Click image to see an enlarged view

Fig. Fig. 38: Rochester 2GC, 2GV Specifications (Cont.)



Click image to see an enlarged view

Fig. Fig. 39: Rochester 2GC, 2GV Specifications (Cont.)

Holding the air horn right side up, measure float drop as follows:

On nitrophyl (black plastic) floats, measure from the air horn gasket to the lip at the toe of the float.

On brass floats, measure from the air horn gasket to the bottom of the float.

Bend the float tang to adjust either type of float.

Rochester 4MC, 4MV, M4MC-4 BBL Carburetors

The Rochester Quadrajet carburetor is a two stage, four-barrel downdraft carburetor. The designation MC or MV refers to the type of choke system the carburetor is designed for. The MV model is equipped with a manifold thermostatic choke coil. The MC model has a choke housing and coil mounted on the side of the float bowl.

The primary side of the carburetor is equipped with 1 3 / 8 diameter bores and a triple venturi with plain tube nozzles. During off idle and part throttle operation, the fuel is metered through tapered metering rods operating in specially designed jets positioned by a manifold vacuum responsive piston.

The secondary side of the carburetor contains two 2 1 / 4 in. bores. An air valve is used on the secondary side for metering control and supplements the primary bores.

The secondary air valve operates tapered metering rods which regulate the fuel in constant proportion to the air being supplied.

ACCELERATOR PUMP

See Figure 40

Click image to see an enlarged view

Fig. Fig. 40: Accelerator pump rod adjustment-Rochester® 4MC and 4MV carburetors

  1. Close the primary throttle valves by backing out the slow idle screw and making sure that the fast idle cam follower is off the steps of the fast idle cam.
  2.  
  3. Bend the secondary throttle closing tang away from the primary throttle lever.
  4.  
  5. With the pump in the appropriate hole in the pump lever, measure from the top of the choke valve wall to the top of the pump stem.
  6.  
  7. To adjust, bend the pump lever while supporting it with a screwdriver.
  8.  
  9. After adjusting, readjust the secondary throttle tang and the slow idle screw.
  10.  

IDLE VENT

This adjustment is not required on 1977-79 carburetors.

After adjusting the accelerator pump rod as specified above, open the primary throttle valve enough to just close the idle vent. Measure from the top of the choke valve wall to the top of the pump plunger stem. If adjustment is necessary, bend the wire tang on the pump lever.

FLOAT LEVEL

See Figure 41

Click image to see an enlarged view

Fig. Fig. 41: Float level adjustment-Rochester® 4MC and 4MV carburetors

With the air horn assembly upside down, measure the distance from the air horn gasket surface (gasket removed) to the top of the float at the toe. Measure at a point 3 / 16 in. back from the top of the float on 1977-79 carburetors.

Make sure the retaining pin is firmly held in place and that the tang of the float is firmly against the needle and seat assembly.

FAST IDLE

See Figures 42 and 43

Click image to see an enlarged view

Fig. Fig. 42: Fast idle speed adjustment-Rochester® 4MC and 4MV carburetors



Click image to see an enlarged view

Fig. Fig. 43: Fast idle cam adjustment-Rochester® 4MC and 4MV carburetors

  1. Position the fast idle lever on the high step of the fast idle cam. Disconnect and plug the vacuum hose at the EGR valve.
  2.  
  3. Be sure that the choke is wide open and the engine warm.
  4.  
  5. Turn the fast idle screw to gain the proper fast idle rpm.
  6.  

CHOKE ROD

Position the cam follower on the second step of the fast idle cam, touching the high step. Close the choke valve directly on models up to 1976. On 1977 models, remove the choke thermostatic cover, and then hold the choke closed by pushing upward on the choke coil lever. Gauge the clearance between the lower edge of the choke valve and the carburetor body on models to 1975, and between the upper edge of the choke valve and the carburetor body on 1976 and 1977 models. Bend the choke rod to obtain the specified clearance. On 1977 models, install the choke thermostatic cover and adjust it to specification when the adjustment is complete. This adjustment requires sophisticated special tools on 1978 and later models, and so is not included here.

AIR VALVE DASHPOT

Seat the vacuum break diaphragm. On 1977-79 models, this requires plugging the bleed purge hole on the back of the diaphragm with tape, and the use of an external vacuum source. Hold the air valve tightly closed on all models. Gauge the clearance between the dashpot rod and the end of the slot in the air valve lever. Bend the rod to adjust. Remove the tape from the bleed purge hole.

CHOKE COIL ROD-1967-76 MODELS
  1. Close the choke valve by rotating the choke coil lever counterclockwise.
  2.  
  3. Disconnect the thermostatic coil rod from the upper lever.
  4.  
  5. Push down on the rod until it contacts the bracket of the coil.
  6.  
  7. The rod must fit in the notch of the upper lever.
  8.  
  9. If it does not, it must be bent on the curved portion just below the upper lever.
  10.  

CHOKE COIL LEVER AND CHOKE THERMOSTATIC COIL-1977-79 MODELS
  1. Remove the three mounting screws and retainers, and pull the thermostatic coil cover assembly off the choke housing and set it aside.
  2.  
  3. Place the fast idle cam follower on the high step of the cam and then push up on the thermostatic coil tang in the choke housing until the choke is closed.
  4.  
  5. Insert a .120 in. plug gauge or rod of that diameter into the hole in the housing located just below the lever. With the choke closed, the lever should just touch the gauge.
  6.  
  7. Adjust the choke rod by changing the angle of the bend it makes just below the choke itself, if necessary.
  8.  
  9. Then, install the coil cover back on the choke housing, making sure that the thermostatic coil engages the tang. Install the three retainers and screws, but do not tighten. With the fast idle cam follower still on the high step of the cam, rotate the cover assembly counterclockwise until the choke closes. Set all models 2 notches lean except 1977 models with manual transmissions; set these three notches lean. Hold the position of the housing while tightening screws evenly.
  10.  

VACUUM BREAK-1967-76 MODELS

See Figures 44 and 45

Click image to see an enlarged view

Fig. Fig. 44: Vacuum break adjustment (rich setting)-Rochester® 4MC and 4MV carburetors



Click image to see an enlarged view

Fig. Fig. 45: Vacuum break adjustment (lean setting)-Rochester® 4MC and 4MV carburetors

  1. Fully seat the vacuum break diaphragm using an outside vacuum source.
  2.  
  3. Open the throttle valve enough to allow the fast idle cam follower to clear the fast idle cam.
  4.  
  5. The end of the vacuum break rod should be at the outer end of the slot in the vacuum break diaphragm plunger.
  6.  
  7. The specified clearance should register from the lower end of the choke valve to the inside air horn wall.
  8.  
  9. If the clearance is not correct, bend the vacuum break link.
  10.  

VACUUM BREAK-1977 MODELS

Adjustment procedures for 1978 and later models require the use of an expensive and sophisticated special tool, so procedures are not included here.

  1. Remove the choke thermostatic cover. Place the fast idle cam follower on the high step of the cam.
  2.  
  3. Where there is a purge bleed hole on the back of the choke vacuum break, put tape over the hole. Then, seat the diaphragm using an outside vacuum source.
  4.  
  5. Push the inside choke coil lever counterclockwise until the tang on the vacuum break lever touches the tang on the vacuum break plunger stem.
  6.  
  7. Place a gauge of the following diameter between the upper edge of the choke butterfly and the inside wall of the air horn:

    California engines: .165"
     
    All other engines: .160"
     

  8.  
  9. If the dimension is incorrect, adjust the screw on the vacuum break plunger stem until all play is taken up and the choke butterfly just touches the gauge when its held vertically.
  10.  
  11. Reconnect the vacuum line to vacuum break port of carburetor, remove the tape from the purge hole (if applied) and reinstall and adjust choke thermostat.
  12.  

CHOKE UNLOADER

See Figure 46

Click image to see an enlarged view

Fig. Fig. 46: Choke unloader adjustment-Rochester® 4MC and 4MV carburetors

Performing this adjustment on 1978 and later models requires sophisticated special tools, so the procedure is not included here.

On 1977 models, make sure the choke thermostatic spring is properly adjusted (see above). Close the choke valve and secure it with a rubber band hooked to the vacuum break lever. Open the primary throttles all the way. Then measure the distance between the air horn and the edge of the choke butterfly. On models up to and including 1976, use the bottom side of the butterfly for this measurement; on 1977 models, use the top side. Bend the fast idle lever tang to achieve the proper opening of the choke.

SECONDARY LOCKOUT-1967-76 MODELS

Completely open the choke valve and rotate the vacuum break lever clockwise. Bend the lever if the measurement between the lever and the secondary throttle exceeds specifications. Close the choke and gauge the distance between the lever and the secondary throttle shaft pin. Bend the lever to adjust.

SECONDARY LOCKOUT-1977-79 MODELS
  1. See the accompanying illustration.
  2.  

AIR VALVE SPRING

See Figure 47

Click image to see an enlarged view

Fig. Fig. 47: Air valve spring setting-Rochester® 4MC and 4MV carburetors

Loosening and tightening the locking screw to adjust the air valve spring requires a hex wrench on 1977 and later model carburetors.

Remove all spring tension by loosening the locking screw and backing out the adjusting screw. Close the air valve and turn the adjusting screw in until the torsion spring touches the pin on the shaft, then turn it the additional number of turns specified. Secure the locking screw.

SECONDARY CLOSING

See Figure 48

Click image to see an enlarged view

Fig. Fig. 48: Secondary closing adjustment-Rochester® 4MC and 4MV carburetors

This adjustment assures proper closing of the secondary throttle plates.

  1. Set the idle as per instructions in Engine Performance And Tune-up . Make sure that the fast idle cam follower is not resting on the fast idle cam.
  2.  
  3. There should be 0.020 in. clearance between the secondary throttle actuating rod and the front of the slot on the secondary throttle lever with the closing tang on the throttle lever resting against the actuating lever.
  4.  
  5. Bend the tang on the primary throttle actuating rod to adjust.
  6.  

SECONDARY OPENING

See Figures 49 through 53

Click image to see an enlarged view

Fig. Fig. 49: Secondary opening adjustment-Rochester® 4MC and 4MV carburetors



Click image to see an enlarged view

Fig. Fig. 50: Rochester 4MV, 4MC, M4MC Specifications



Click image to see an enlarged view

Fig. Fig. 51: Rochester 4MV, 4MC, M4MC Specifications (Cont.)



Click image to see an enlarged view

Fig. Fig. 52: Rochester 4MV, 4MC, M4MC Specifications (Cont.)



Click image to see an enlarged view

Fig. Fig. 53: Rochester 4MV, 4MC, M4MC Specifications (Cont.)

  1. Open the primary throttle valves until the actuating link contacts the upper tang on the secondary lever.
  2.  
  3. With two point-linkage, the bottom of the link should be in the center of the secondary lever slot.
  4.  
  5. With three point linkage, there should be 0.070 in. clearance between the link and the middle tang.
  6.  
  7. Bend the upper tang on the secondary lever to adjust as necessary.
  8.  

Holley 4150-4 BBL Carburetor

The 4150 carburetor has been both an end and center inlet design.

CHOKE

The model 4150 employs a remotely located choke. To adjust, disconnect the choke rod at the choke lever and secure the choke lever shut. Bend the rod so that when the rod is depressed to the contact stop, the top is even with the bottom of the hole in the choke lever.

FLOAT LEVEL

Position the car on a flat, level surface and start the engine. Remove the sight plugs and check to see that the fuel level reaches the bottom threads of the sight plug port. A tolerance of 1 / 32 in. is acceptable. To change the level, loosen the fuel inlet needle locking screw and adjust the nut. Turning it clockwise lowers the fuel level and counterclockwise raises it. Turn the nut 1 / 6 of a turn for each 1 / 16 in. desired change. Open the primary throttle slightly to assure a stabilized adjusting condition on the secondaries. There is no required float drop adjustment.

FAST IDLE

Open the throttle and place the choke plate fast idle lever against the top step of the fast idle cam. Bend the fast idle lever to obtain the specified throttle plate opening.

CHOKE UNLOADER

Adjustment should be made with the engine not running. Fully open and secure the throttle plate. Force the choke valve toward a closed position, so that contact is made with the unloader tang. Bend the choke rod to gain the specified clearance between the main body and the lower edge of the choke valve.

ACCELERATOR PUMP

With the engine OFF, block the throttle open and push the pump lever down. Clearance between the pump lever arm and the spring adjusting nut should be 0.015 in. minimum. Turn the screw or nut to adjust this clearance.

SECONDARY THROTTLE VALVE

Close the throttle plates, then turn the adjustment screw until it contacts the throttle lever. Advance the screw 1 / 2 turn more.

AIR VENT VALVE

Close the throttle valves and open the choke valve so that the throttle arm is free of the idle screw. Bend the air vent valve rod to obtain the specified clearance between the choke valve and seat. Advance the idle speed screw until it touches the throttle lever, then advance it 1 1 / 2 turns.

VACUUM BREAK

Secure the choke valve closed and the vacuum break against the stop. Bend the vacuum break link to gain the specified clearance between the main body and the lower edge of the choke valve.

Rochester M2ME and E2ME-2 BBL Carburetors
FLOAT

See Figures 54 and 55

Click image to see an enlarged view

Fig. Fig. 54: Adjusting the float level-Rochester® M2ME and E2ME carburetors



Click image to see an enlarged view

Fig. Fig. 55: Holley 4150 Specifications

  1. Remove the air horn from the throttle body.
  2.  
  3. Using your fingers, hold the retainer in place and push the float down into light contact with the needle.
  4.  
  5. Measure the distance from the toe of the float (furthest from the hinge) to the top of the carburetor (gasket removed).
  6.  
  7. To adjust, remove the float and gently bend the arm to specifications. After adjustment, check the float alignment in the chamber. On engines equipped with the C-4 or the CCC system, where the float level varies more than 1 / 16 in. from specifications, adjust the float as follows. Float too high:
  8.  
  9. Hold the retainer firmly in place and push down the center of the float pontoon until the correct setting is obtained. Float too low:
  10.  
  11. Lift out the meter rods and remove the solenoid connector screw.
  12.  
  13. Turn the lean mixture solenoid screw clockwise until the screw is bottomed lightly in the float bowl. [cf2]Count and record the number of turns before the screw is bottomed.
  14.  
  15. Turn the screw counterclockwise and remove it. Lift the solenoid and the connector from the float bowl.
  16.  
  17. Remove the float and bend the arm up to adjust it. Put the float back in and check its alignment.
  18.  
  19. Installation is in the reverse order of removal. Make sure that the solenoid lean mixture screw is backed out of the float bowl EXACTLY the same number of turns as were recorded in Step 2.
  20.  

PUMP

See Figure 56

Click image to see an enlarged view

Fig. Fig. 56: Pump adjustment-Rochester® M2ME and E2ME carburetors (except C-4 or CCC equipped models)

All 1980-81 engines equipped with the C-4 or the CCC system have a non-adjustable pump lever. No adjustments are either necessary or possible.

  1. With the throttle closed and the fast idle screw off the steps of the fast idle cam, measure the distance from the air horn casting to the top of the pump stem.
  2.  
  3. To adjust the lever, support it firmly with a screwdriver, then bend it to obtain the proper specifications.
  4.  
  5. When the adjustment is correct, open and close the throttle a few times to check the linkage movement and alignment.
  6.  

CHOKE COIL LEVER

See Figure 57

Click image to see an enlarged view

Fig. Fig. 57: Adjusting the choke coil lever-Rochester® M2ME and E2ME carburetors

To complete this procedure you will need a Stat Cover Retainer kit; available at most auto parts suppliers.

  1. Drill out and remove the rivets which retain the choke housing cover and then remove the thermostatic cover and coil assembly from the choke housing.
  2.  
  3. Place the fast idle cam follower on the high step of the fast idle cam.
  4.  
  5. Close the choke valve by pushing up on the thermostatic coil tang (counterclockwise).
  6.  
  7. Insert a drill or gauge of the specified size into the hole in the choke housing. The lower edge of the choke lever should be just touching the side of the gauge.
  8.  
  9. If the choke lever is not touching the side of the gauge, bend the choke rod until you see that it does.
  10.  

FAST IDLE

See Figure 58

Click image to see an enlarged view

Fig. Fig. 58: Adjusting the fast idle with the carburetor removed from the engine-Rochester® M2ME and E2ME carburetors

  1. Set the ignition timing and curb idle speed. Disconnect and plug any hoses as directed on the emission control sticker.
  2.  
  3. Place the fast idle screw on the highest step of the fast idle cam.
  4.  
  5. Start the engine and adjust the engine speed to specifications with the fast idle screw.
  6.  

FAST IDLE CAM (CHOKE ROD)

See Figure 59

Click image to see an enlarged view

Fig. Fig. 59: Fast idle cam (choke rod) adjustment-Rochester® M2ME and E2ME carburetors

A special angle gauge should be used. If it is not available, an inch measurement can be used.

  1. Adjust the choke coil lever and the fast idle as previously detailed.
  2.  
  3. Rotate the degree scale until it is zeroed.
  4.  
  5. Close the choke valve completely and place the magnet on top of it.
  6.  
  7. Center the bubble.
  8.  
  9. Rotate the scale so that the specified degree is opposite the pointer.
  10.  
  11. Place the fast idle screw on the second step of the cam, against the rise of the high step.
  12.  
  13. Close the choke by pushing up on the choke coil lever or the vacuum break lever tang. You may hold it in position with a rubber band.
  14.  
  15. To adjust, bend the tang on the fast idle cam until the bubble is centered.
  16.  

FRONT VACUUM BREAK

See Figure 60

Click image to see an enlarged view

Fig. Fig. 60: Front vacuum break adjustment-Rochester® M2ME and E2ME carburetors

  1. Follow Steps 1-5 of the "Fast Idle Cam Adjustment" procedure.
  2.  
  3. Set the choke vacuum diaphragm using an outside vacuum source.
  4.  
  5. Close the choke valve by pushing up on the choke coil lever or the vacuum break lever. You may hold it in position with a rubber band.
  6.  
  7. To adjust, turn the screw in or out until the bubble in the gauge is centered.
  8.  

REAR VACUUM BREAK

See Figure 61

Click image to see an enlarged view

Fig. Fig. 61: Rear vacuum break adjustment-Rochester® M2ME and E2ME carburetors

  1. Follow Steps 1-3 of the "Front Vacuum Break Adjustment" procedure.
  2.  
  3. To adjust, use a 1 / 8 in. Allen wrench to turn the screw in the rear cover until the bubble is centered. After adjusting, apply silicone sealant RTV over the screw head to seal the setting.
  4.  

UNLOADER

See Figures 62, 63 and 64

Click image to see an enlarged view

Fig. Fig. 62: Unloader adjustment-Rochester® M2ME and E2ME carburetors



Click image to see an enlarged view

Fig. Fig. 63: Rochester M2ME, E2ME Specifications



Click image to see an enlarged view

Fig. Fig. 64: Rochester M2ME, E2ME Specifications (Cont.)

  1. Follow Steps 1-5 of the "Fast Idle Cam Adjustment" procedure.
  2.  
  3. If they have been previously removed, install the choke thermostatic cover and the coil assembly into the choke housing.
  4.  
  5. Close the choke valve by pushing up on the tang on the vacuum break lever (you may hold it with a rubber band).
  6.  
  7. Hold the primary throttle valves wide open.
  8.  
  9. To adjust, bend the tang on the fast idle lever until the bubble on the gauge is centered.
  10.  

Rochester M4ME and E4ME-4 BBL Carburetors

Float, pump, choke coil lever, fast idle, fast idle cam (choke rod), front and rear vacuum break and unloader adjustments on these two carburetors are identical to those detailed in the preceding "M2ME and E2ME" section. Please refer to them. There are, however, a number of procedures that apply only to these 4 bbl carburetors.

AIR VALVE ROD

See Figure 65

Click image to see an enlarged view

Fig. Fig. 65: Adjusting the air valve rod-Rochester® M4ME and E4ME carburetors

  1. Using an outside vacuum source, seat the choke vacuum diaphragm. Put a piece of tape over the purge bleed hole if so equipped.
  2.  
  3. Close the air valve completely.
  4.  
  5. Insert the gauge between the rod and the end of the slot in the lever.
  6.  
  7. Bend the rod to adjust the clearance.
  8.  

SECONDARY LOCKOUT

See Figure 66

Click image to see an enlarged view

Fig. Fig. 66: Secondary lockout adjustment-Rochester® M4ME and E4ME carburetors

  1. Pull the choke wide open by pushing out on the choke lever.
  2.  
  3. Open the throttle until the end of the secondary actuating lever is opposite the toe of the lockout lever.
  4.  
  5. Measure the clearance between the lockout lever and the secondary lever.
  6.  
  7. Bend the lockout pin until the clearance is in accordance with the proper specifications.
  8.  

SECONDARY CLOSING

See Figure 67

Click image to see an enlarged view

Fig. Fig. 67: Secondary closing adjustment-Rochester® M4ME and E4ME carburetors

  1. Make sure that the idle speed is set to the proper specifications.
  2.  
  3. The choke valve should be wide open with the cam follower off of the steps of the fast idle cam.
  4.  
  5. There should be 0.020 in. clearance between the secondary throttle actuating rod and the front of the slot on the secondary throttle lever with the closing tang on the throttle lever resting against the actuating lever.
  6.  
  7. To adjust, bend the secondary closing tang on the primary throttle actuating rod.
  8.  

SECONDARY OPENING

See Figure 68

Click image to see an enlarged view

Fig. Fig. 68: Secondary opening adjustment-Rochester® M4ME and E4ME carburetors

  1. Open the primary throttle valves until the actuating link contacts the upper tang on the secondary lever.
  2.  
  3. With the two point linkage, the bottom of the link should be in the center of the secondary lever slot.
  4.  
  5. With the three point linkage, there should be 0.070 in. clearance between the link and the middle tang.
  6.  
  7. To adjust, bend the upper tang on the secondary lever.
  8.  

AIR VALVE SPRING

See Figure 69

Click image to see an enlarged view

Fig. Fig. 69: Adjusting the air valve spring-Rochester® M4ME and E4ME carburetors

To adjust the air valve spring wind-up, loosen the Allen head lockscrew and turn the adjusting screw counterclockwise so as to remove all spring tension. With the air valve closed, turn the adjusting screw clockwise the specified number of turns after the torsion spring contacts the pin on the shaft. Hold the adjusting screw in this position and tighten the lockscrew.

 
label.common.footer.alt.autozoneLogo