GM 17112747 Carburetor Asm

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The carburetor is attached to the top of the intake manifold by two or four nuts. These fasteners can sometimes work loose through normal engine operation and cause a vacuum leak. To properly tighten the carburetor mounting nuts, a torque wrench is necessary. If you do not own one, they can usually be rented on a daily basis. Remove the air cleaner assembly, tagging each hose to be disconnected with a piece of numbered tape to make reassembly easier. Locate the mounting nuts at the base of the carburetor. Decide what special tools or adapters will be necessary, if any, to tighten the nuts with a properly sized socket and the torque wrench. Tighten the nuts to a torque of about 12 ft-lbs. Do not overtighten the nuts, as this may cause the threads to strip. If you suspect a vacuum leak exists at the bottom of the carburetor, get a length of spare hose about the diameter of fuel hose. Start the engine and place one end of the hose next to your ear as you probe around the base of the carburetor with the other end. You will be able to hear a hissing sound if a leak exists. A soapy water solution brushed around the suspect area can also be used to pinpoint pressure leaks. If, after the nuts are properly tightened, a vacuum leak still exists, the carburetor must be removed and a new gasket used. After tightening the nuts, reinstall the air cleaner, connecting all hoses to their original positions.

Pre 1972 models,Remove the air cleaner and plug the air cleaner.sensor vacuum take-off port in the carburetor. Start the engine or apply suction to the diaphragm vacuum tube. Remove the choke rod from the lever and install a rubber band to the lever to hold the choke towards the closed position. Slowly open the accelerator until the choke is closed as far as the vacuum break link reaction will permit, and the idle is determined by the high step of the fast idle cam. Release the accelerator. With the condition of 4 maintained, insert a gauge of the specified thickness between the air horn and the choke blade. Bend the rod or tang as necessary to obtain the specified dimension. 1972 models onward: Remove the air cleaner and plug the air cleaner sensor vacuum take-off port in the carburetor. Using an external suction source, apply suction to the vacuum break diaphragm until the plunger is fully seated. With the diaphragm fully seated, push the choke valve towards the closed position and place a gauge of the specified thickness between the air horn and the choke blade. Bend the vacuum break rod if necessary to obtain the specified dimension.

First, back off the adjustment screw until the throttle plates are fully closed. Then, rotate the adjustment screw until it just touches the throttle lever, and then rotate it an additional half-turn.

If the information given on the Decal label has superseded the information given in the Specifications, the Decal label should be assumed to be correct. For 1975 models, have the engine at normal operating temperature with the ignition settings correct. Disconnect the fuel tank hose from the vapor canister. Connect a tachometer to the engine and switch the air conditioning off. Turn the idle speed screw until the engine is running at the speeds specified with manual transmission in Neutral and automatic transmission in Drive. The mixture screws are fitted with limiter caps which restrict their movement between t and 3/4 turn lean. Any adjustment should be kept to this but where the carburetor has been overhauled or new components fitted then the caps should be broken off and the following operations carried out. Have the engine at normal operating temperature with air conditioning off and a tachometer connected to the engine. Disconnect the fuel tank hose from the vapor canister. Adjust the idle speed screw until the initial idle speed is obtained. Now unscrew the mixture screws equally until maximum idle speed is achieved. Readjust the idle speed screw again to obtain initial idle speed. Screw in the mixture screws equally until final idle speed (lean drop) is obtained. For 1976 models and later, have the engine at normal operating temperature with ignition settings correct and emission control systems operating correctly. Set the idle speed screw on the low step of the fast idle cam. Turn the idle speed screw to set the curb (initial idle speed) to specification or vehicle Decal. Where a solenoid is fitted to the carburetor, carry out the operations described and then with the solenoid energized, the lead disconnected from the air conditioner compressor. the air conditioner on, open the throttle to allow the solenoid plunger to extend fully. Turn the solenoid hexagonal headed bolt until the idle speed is 700 rpm (manual) or 650 rpm (automatic). Reconnect the compressor lead on completion. 2GC carburetors are fitted with a solenoid when the vehicle is equipped with automatic transmission or air conditioning.

Loosen the 3 retaining screws and remove the choke coil cover and coil assembly from the choke housing. Place the cam follower lever on the highest step of the fast idle cam. Using an outside source of suction, seat the diaphragm unit. Push up on the inside choke coil lever until the tang on the vacuum break lever contacts the tang on the plunger. Measure between the upper edge of the choke valve and the inside of the air horn wall. Turn the adjustment screw on the vacuum break plunger to obtain the specified dimension. Install the vacuum hose on completion.

Hold the throttle lever wide open, using a rubber band to keep it in place, then fully compress the pump lever, meaning the lever is pressed down. Measure the gap between the spring adjusting nut and the pump lever arm. If necessary, adjust to obtain a gap of 0.015 in by turning the nut or screw while preventing the opposite end from turning. After adjustment, close the throttle lever then partly open it again. Any movement of the throttle lever should be noticed at the operating lever spring end, indicating correct pump tip-in.

With this type of electrically heated automatic choke, ensure that the coil assembly inside the choke housing has the coil tang contacting the bottom side of the inner face of the choke coil lever pickup arm. Then, position the fast idle cam follower on the high step of the cam. Following this, rotate the cover and coil assembly counterclockwise until the choke valve just closes. Finally, align the index marks (center) and install the cover and screws. It's important to note that the ground contact for the electrically heated choke is through a metal plate at the rear of the choke assembly. Avoid installing a gasket between the cover and housing as this will interrupt the circuit.

When a carburetor develops faults after considerable mileage, it's often more cost-effective to replace the entire unit rather than replace individual components. However, if you decide to proceed with the rebuilding process, start by obtaining a repair kit containing the necessary gaskets and components, and follow these steps: Initially, loosen the fuel inlet fitting, fuel bowl sight plugs, and the needle and seat lockscrews. Remove the primary and secondary fuel bowls, metering bodies, and associated gaskets, disconnect the secondary throttle operating rod, throttle operating assembly, and gasket. Disconnect the hose at the vacuum break and remove the throttle body, throttle body to main body screws, and gasket. Loosen the inlet needle and seat lockscrew, then remove the needle and seat assembly. Remove the float after removing the hinge pin retainer, and slide it out along with the spring if necessary. Remove the sight plug and gasket, inlet fitting, fuel filter, spring, and gaskets. From the primary bowl, remove the air valve assembly (if applicable), pump diaphragm components, main metering jets, power valves, idle mixture screws, and seals. Disassemble the secondary throttle operating assembly, including the diaphragm cover, spring, and diaphragm. Remove the vacuum break retaining screws and assembly, disconnecting the link at the choke lever. Remove the choke lever retaining clip, lever, and fast idle cam. Remove the pump discharge nozzle components, discharge check valve, and, if further dismantling is required, file off the staked ends of the shaft screws and remove them, along with the choke rod and seal. Remove the throttle body components, including the pump operating lever assembly, spring bolt, nut, idle speed screw, secondary throttle shaft diaphragm lever, primary throttle shaft fast idle cam lever, key, and the secondary locknut throttle connecting link from the shaft levers. File off the staked ends of the throttle plate attaching screws, remove the screws and plates, and withdraw the shafts from the flange. Remove the throttle lever accelerator pump cam and vacuum break hose. Clean all metal parts in a suitable cold solvent, avoiding non-metallic parts, rubber, and plastic components. Do not probe the jets; instead, blow them through with clean, dry compressed air. Inspect all parts for damage, wear, cracks, or distortion, replacing as necessary, and discard gaskets. Check the secondary throttle operating diaphragm's functionality. Assembly is essentially the reverse of the removal process, with specific considerations for throttle shaft bushings, throttle valve orientation, idle speed screw adjustment, choke valve freedom of movement, and proper installation of idle mixture screws with new seals. Ensure accurate float adjustment, secondary throttle stop valve, fast idle cam, accelerator pump, choke unloader, and vacuum break adjustments as needed.

When dealing with a carburetor that has developed faults after extensive use, replacing the entire unit is often a more cost-effective option than a complete disassembly and component replacement. However, if the decision is made to strip and rebuild the carburetor, start by obtaining a repair kit containing essential gaskets and parts, and follow this sequence: First, bend back the lockwasher tabs and remove the idle stop solenoid if applicable. Next, disconnect the choke lever from the vacuum break diaphragm link and the vacuum break link from the diaphragm plunger. The diaphragm plunger stem spring can remain in place. Proceed to disconnect the vacuum break hose from the tube and remove the diaphragm from the air horn by unscrewing two retaining screws. Remove the fuel inlet filter nut, filter, spring, and two gaskets, then remove the pump rod from the throttle lever after removing the retaining clip. Rotate the upper pump lever counterclockwise and remove the pump rod from the lever. Remove the fast idle cam and its retaining screw, then hold the choke open and remove the choke rod from the upper choke lever. Continue by removing the air horn from the float bowl using eight screws and removing the float hinge pin, float, splash shield, and float needle. Unscrew the float needle seat and remove the gasket, followed by removing the air horn to float bowl gasket. Depress the power piston shaft to eject the piston from the casting with the help of the spring. Remove the inner pump lever retaining screw and take off the outer pump lever and plastic washer from the air horn, placing the plunger in gasoline to prevent the rubber from drying out. If the choke shaft or valve needs replacement, remove the two staked screws, then remove the valve, shaft, and lever from the air horn. Remove the pump plunger return spring from the pump well, followed by the inlet check ball where applicable, and the pump inlet screen from the bottom of the float bowl where applicable. Unscrew the main jets, power valve, and gaskets, then remove the cluster and gasket using three screws and washers, taking note of the fiber washer on the center screw. Remove the pump discharge spring retainer, the spring, and the check ball. Finally, remove the throttle body to bowl attaching screws and take off the body and gasket. Further dismantling is not recommended, but if it's essential to remove the idle mixture needles, pry out the plastic limiter caps, count the number of turns to bottom the needles, and fit replacements in the same position. After cleaning all metal parts in a suitable cold solvent, avoiding immersion of rubber, plastic, vacuum break assembly, or idle stop solenoid, and blowing clean the jets with compressed air, examine all fixed and moving parts for cracks, wear, distortion, or damage, replacing as necessary, along with discarding all gaskets and fuel inlet filter. The assembly process is essentially the reverse of removal, with specific points to note, such as adjusting idle mixture screws, choke valve positioning, float adjustments, and the even tightening of air horn screws. Finally, after reassembly, perform all necessary settings and adjustments.

Always adjust choke coil lever before carrying out the following operations. Turn the fast idle screw in until it contacts the fast idle cam follower lever, then turn in 3 full turns more. Place the lever on the second step of the fast idle cam against the rise of the high step. Push upwards on the choke coil lever inside the housing to close the choke valve. Measure between the upper edge of the choke valve and the air horn wall. If necessary, bend the tang on the fast idle cam to adjust, but ensure that the tang lies against the cam after bending. Re-check the fast idle adjustment.

With the engine turned off, place the throttle on the high step of the fast idle cam. Disconnect and plug the vacuum hose at the EGR valve. Also, disconnect and plug the vacuum hose at the distributor. Start the engine in 'Park' or 'Neutral' without touching the accelerator pedal. Adjust the fast idle speed screw to the rpm specified on the emission Decal. Open the throttle to release the fast idle cam and turn off the engine. Finally, unplug and reconnect the vacuum hoses to the EGR valve and distributor.

With the hot air heater type of choke, install the choke coil and cover assembly with a gasket between the cover and housing. The tang in the coil must be installed in the slot inside the choke coil lever pick-up arm. Place the fast idle cam follower on the highest step of the fast idle cam then rotate the cover counterclockwise until the choke just closes. Align the index mark on the cover with the specified point (2 notches lean) on the choke housing then tighten the retaining screws.

Hold the choke valve open then pull down on the coil rod to the end of its travel for pre-1972 models. The top of the rod end which slides in the hole in the choke lever, should be even with the bottom of the choke lever hole. Bend the rod at the point shown to adjust. Connect the rod to the choke lever and install the retaining clip. Check that the choke operates freely. For 1972 models onward, hold the choke valve plate fully open. Disconnect the thermostatic coil rod from the upper lever and push down on the rod as far as it will go. The top of the rod should be level with the bottom of the hole in the choke lever. Adjust if necessary by bending the rod.

Idle speed adjustment must be carried out after the engine has fully warmed up. The air cleaner must be fitted, except where otherwise specified, and it is essential that the ignition timing and dwell angle are correctly set. All emission control systems must also be functioning correctly. In order to check engine speed, an external tachometer must be connected, following the manufacturer's instructions. Note: if the information given on the Decal label has superseded the information given in Specifications, the Decal label should be assumed to be correct. Disconnect the electrical lead from the idle speed solenoid (if so equipped). Adjust the base idle speed screw to the rpm specified on the emission label. The shift selector on automatic transmissions should be in Drive, and manual transmissions should be in Neutral. The idle mixture screws have been preset at the factory and sealed. The only time the mixture screws will need adjusting is in the case of a major carburetor overhaul, throttle body replacement or in the case of a high emissions reading by official inspections. Because the mixture screws are sealed, an artificial enrichment procedure using propane gas is required to check the mixture. Adjusting the mixture by any other means may be a violation of law.

1972 models onwards use an external source of suction to seat the choke vacuum break diaphragm. Open the throttle slightly so that the cam follower clears the fast idle cam steps, then rotate the vacuum break lever towards the closed direction. Ensure that the vacuum break rod is in the outer end of the slot in the diaphragm plunger. A rubber band can be used to hold the vacuum break lever in position. Measure the distance from the lower edge of the choke valve to the air horn wall. Check this against the figure shown in Specifications and if adjustment is needed, bend the link rod.

Using a separate source of suction, such as the mouth or a small hand pump, seat the vacuum break diaphragm. Cover the vacuum break bleed hole with a piece of masking tape. Place the idle speed screw on the high step of the fast cam idle. Hold the choke coil lever inside the choke housing towards the closed choke position. Check the dimension between the upper edge of the choke valve and the air horn wall. If adjustment is required to obtain the specified dimension, bend the vacuum break rod. Remove the masking tape on the vacuum unit bleed hole and reconnect the vacuum hose.

Place the cam follower lever on the highest step of the fast idle cam. Turn the fast idle screw out until the primary throttle valves are closed. Turn in the fast idle screw to contact the lever then screw in a further 3 full turns. Connect a tachometer to the engine which should be at the normal operating temperature. Place the transmission in Park or Neutral. Disconnect and plug the vacuum hose at the EGR valve. Position the cam follower on the highest step of the fast idle cam. Turn the fast idle screw to achieve the specified fast idle. Remake the original connections, remove the tachometer and switch off the engine.

Place the cam follower on the second step of the fast idle cam and against the high step. Then, rotate the choke valve towards the closed position by turning the external lever counterclockwise. Check that the dimension between the lower edge of the choke valve and the air horn wall (at the lever end) is as specified. If adjustment is required, bend the choke rod.

Remove three screws and retainers and remove the thermostatic coil cover. gasket and inside baffle plate assembly. Place the idle speed screw on the highest step of the fast idle cam. Close the choke valve by pushing up on the intermediate choke lever. The edge of the coil lever inside the choke housing must align with the edge of the gauge. If necessary, bend the choke rod to adjust.

When a carburetor develops faults after considerable mileage, it's often more cost-effective to replace the entire unit rather than replacing individual components. However, if you decide to strip and rebuild the unit, begin by obtaining a repair kit containing the necessary gaskets and components, and follow these steps: If the carburetor features an idle stop solenoid, remove the solenoid and bracket assembly by undoing the bracket retaining screws. Remove the upper choke lever by unscrewing one screw, rotating it to detach, and disconnect it from the choke rod. Remove the choke rod from the lower lever inside the float bowl by holding the lever outward with a small screwdriver and twisting the rod counterclockwise. Remove the vacuum hose from the front vacuum break unit. Remove the small screw securing the metering rod hanger, then remove the secondary metering rods and hanger. Using a suitable drift, drive the small pump lever pivot roll pin inward to facilitate lever removal. Detach the float bowl by removing 2 long screws, 5 short screws, and 2 countersunk head air horn screws, leaving the gasket in place. Do not attempt to remove the small tubes protruding from the air horn. Remove the front vacuum break bracket screws and lift off the unit, disconnecting the air valve dashpot rod from the diaphragm assembly and the air valve lever. If necessary, remove the staked choke valve attaching screws, then remove the choke valve and shaft from the air horn, avoiding removal of the air valve and air valve shaft. Remove the air horn gasket from the float bowl, being cautious not to distort the springs holding the main metering rods. Remove the pump plunger and pump return spring from the pump well. Depress the power piston stem, release it to remove it along with the metering rods, and remove the power piston spring from the well. Remove the metering rods from the power piston by disconnecting the tension springs and rotating the rods. Remove the plastic filler block over the float valve and slide out the float assembly and needle. Remove the needle seat and gasket, the cover screws, and carefully lift out the metering rod and filler spool from the float bowl. Note that the adjustable part-throttle (APT) metering rod assembly should not be interfered with. Remove the primary main metering jets and the pump discharge check ball retainer and ball. Remove the rear vacuum break hose and bracket retaining screws and extract the vacuum break rod from the slot in the plunger head. Press down on the fast idle cam to remove the vacuum break rod, disengage it from the hole in the intermediate lever, and remove the choke cover attaching screws and retainers, along with the cover and gasket. Remove the choke housing assembly from the float bowl by removing the retaining screw and washer, the secondary throttle valve lock-out lever, the lower choke lever by inverting the float bowl, the plastic tube seal from the choke housing, and, if necessary, the intermediate choke shaft from the choke housing, followed by the fast idle cam if applicable. Remove the fuel inlet filter nut, gasket, and filter from the float bowl, the pump well fill slot baffle and the secondary air baffle if required. Remove the throttle body attaching screws, lift off the float bowl, and remove the insulator gasket. Remove the pump rod from the lever on the throttle body, and if it's essential to remove the idle mixture needles, pry out the plastic limiter caps, count the number of turns to bottom the needles, and fit replacements in the same position. New limiter caps should be fitted after running adjustments. Clean all metal parts in a suitable cold solvent, avoiding rubber parts, plastic components, pump plungers, filler spools or aneroids, and vacuum breaks. Do not probe the jets; instead, blow through them with clean, dry compressed air. Inspect all parts for damage, wear, cracks, or distortion, replacing as necessary, and discard gaskets and the fuel inlet filter. Assembly is essentially the reverse of the removal process, but several key points should be noted: If new idle mixture screws are used, and the original setting is unknown, install the screws finger-tight to seat them, then back off 4 full turns. Ensure correct orientation of plastic insert cup seals, proper assembly of choke components, accurate float adjustment, and tight air horn screw sequence. Upon completion of assembly, adjust the front and rear vacuum breaks, fast idle cam, choke coil lever, and automatic choke coil. Replacement of the APT metering rod should only occur if the assembly is damaged or the aneroid has failed, following specific steps to ensure proper installation.

Loosen the 3 retaining screws and remove the cover and coil assembly from the choke housing. Push up on the thermostatic coil tang (counterclockwise) until the choke valve is closed. Check that the choke rod is at the bottom of the slot in the choke lever. Insert a plug gauge (an unmarked drill shank is suitable) of the specified size in the hole in the choke housing. The lower edge of the choke coil lever should just contact the side of the plug gauge. If necessary, bend the choke rod at the point shown.

When a carburetor experiences issues after extensive use, it is often more cost-effective to replace the entire unit rather than fully disassembling and replacing individual components. However, if the decision is made to disassemble and rebuild the carburetor, begin by obtaining a repair kit containing necessary gaskets and parts. Follow this sequence: If the carburetor has a solenoid (related to automatic transmission or air conditioning), remove it by bending back lockwasher tabs and unscrewing the large nut securing the solenoid to the bracket, avoiding solvent immersion. Proceed to remove the fuel inlet filter components, disconnect the lower end of the pump rod from the throttle lever, and remove the upper end of the pump rod from the pump lever. Disconnect the vacuum break diaphragm hose and remove the diaphragm assembly along with the vacuum break lever from the choke shaft's end, and the intermediate choke rod from the vacuum break lever on the coil housing. Remove the fast idle cam and its retaining screw, then lift off the air horn by removing the eight attaching screws and lockwashers. Extract the float hinge pin, float, float needle, and pull clip (if applicable). Unscrew the float needle seat and remove the gasket. Depress the power piston to release it and remove the pump plunger assembly and inner pump lever by loosening set screws. If overhauling the pump assembly, break off the flattened end of the pump plunger stem. Remove the outer lever, shaft assembly, and plastic washer from the pump plunger shaft. Take off the air horn gasket and the fuel inlet baffle. Carefully remove the choke valve, retaining screws may need dressing for removal, and the choke valve shaft. Extract the fast idle cam rod and lever from the shaft. Remove the pump plunger return spring and invert the bolt to remove the aluminum ball. Unscrew the main metering jets, power valve, and gaskets, followed by the removal of the venturi cluster using three screws and gasket. Remove the pump discharge spring retainer, spring, and check ball from the discharge passage. Extract the three large throttle body to bowl attaching screws and lockwashers, removing the throttle body and gasket. Remove the thermostatic choke coil cover and gasket, avoiding the removal of the cap baffle beneath the coil cover, and take off the choke housing baffle plate. From inside the choke housing, remove the attaching screws, housing, and gasket. Remove the screw from the end of the intermediate choke shaft, then remove the choke lever, inner choke coil lever and shaft assembly, and the rubber dust seal. Further disassembly, especially concerning throttle valves or shafts, is discouraged due to potential complications in reassembly. However, if necessary, remove the idle mixture needles by breaking off the plastic limiter caps and note the number of turns to bottom the needles for replacements. New limiter caps should be fitted after running adjustments. Clean all metal parts in a suitable cold solvent, avoiding immersion of rubber, plastic parts, diaphragm assemblies, or pump plungers to prevent permanent damage. Do not probe the jets; instead, blow through them with clean, dry compressed air. Inspect all fixed and moving parts for cracks, distortion, wear, or damage, replacing as required. Discard all gaskets and the fuel inlet filter. Assembly is essentially the reverse of removal; however, specific points to note include the installation of new idle mixture screws, proper orientation of the rubber dust seal in the choke housing cavity, choke valve positioning, float level and float drop checks, proper venturi cluster assembly, and the tightening of air horn screws as indicated for 2GV carburetors. After reassembly, perform relevant settings and adjustments.

When a carburetor experiences issues after extensive use, it is often more cost-effective to replace the complete unit rather than fully disassembling and replacing individual components. However, if the decision is made to disassemble and rebuild the carburetor, begin by obtaining a repair kit containing necessary gaskets and parts. Follow this sequence: Remove the solenoid (if equipped) from the float bowl by unscrewing the solenoid and bracket assembly screws, avoiding immersion in carburetor cleaner. Proceed to remove the choke lever at the top of the carburetor by removing the retaining screw and rotating the choke lever to release the choke rod. Remove the choke rod from the lower lever by twisting it counterclockwise while holding the lower lever outward. Note the position of the accelerator pump rod on its lever, then remove the pump lever by driving the pivot pin inward slightly. Remove the seven screws attaching the top air horn assembly to the bowl, lifting the air horn straight up and off the float bowl. From the air horn assembly, remove the vacuum break hose and the vacuum break control and bracket assembly. Lift the air horn gasket from the top of the float bowl assembly, taking care not to distort the spring holding the main metering rods in place. Remove the pump plunger from the pump well, followed by the plunger return spring. Remove the power piston and metering rods from the well by depressing and releasing the piston to snap it free. Remove the metering rods from the power piston by disconnecting the spring from each rod and rotating the rod to remove it from the hanger. Remove the plastic filler block over the float valve and then the float assembly, float needle, retaining pin, seat, and gasket. Remove the main metering jets if necessary, as well as the pump discharge check ball retainer and check ball, and the pump well fill slot baffle. The choke cover, held by rivets, is removed by drilling out the rivet heads. Remove the choke assembly retainers, cover gasket, and choke cover assembly from the main housing, avoiding the removal of the baffle beneath the choke cover coil. The choke housing can be removed from the float bowl by removing the retaining screw inside the housing. Remove the rear vacuum break rod from the intermediate choke lever. To remove the intermediate choke shaft, remove the retaining screw inside the choke housing and the coil lever from the shaft. Slide the intermediate shaft outward and remove the fast idle cam from the shaft. Remove the cup seal from the float bowl insert without removing the insert itself. Turn the float bowl upside down and remove the choke lever from inside the cavity. From the float bowl assembly, remove the fuel inlet nut, gasket, check valve filter, and spring. Separate the throttle body from the float bowl by removing the attaching screws and remove the pump rod from the throttle lever. Do not remove the plugs covering the idle mixture needles unless it is necessary to replace the mixture screws; cleaning the mixture passages should suffice. Clean all metal parts in a suitable cold solvent, excluding rubber parts, plastic parts, the vacuum break assembly, or the idle stop solenoid. Avoid probing the jets and instead blow them clean with dry compressed air. Inspect all fixed and moving parts for cracks, distortion, wear, or damage, replacing parts as needed, and discard all gaskets and the fuel inlet filter. Assembly is essentially the reverse of the removal procedure, with specific points to note, such as adjusting the choke coil cover assembly after inside coil lever adjustment, adjusting float level, and tightening the air horn attaching screws evenly in the specified sequence.

Hold the throttle valve open with the fingers. Using a suitable gauge, check that the clearance between the edge of the choke valve plate and the air horn wall is as specified. If necessary, bend the tang to adjust.

Adjust the engine idle speed. Hold the choke valve wide open with the cam follower lever off the steps of the fast idle cam. Measure the clearance between the slot in the secondary throttle valve pick-up lever and the secondary actuating rod. If adjustment is necessary, bend the secondary tang on the primary throttle lever to obtain the specified clearance (0.020 inch).

With the fast idle cam follower off the steps of the fast idle cam, back out the idle speed screw until the throttle valves are completely closed in the bore. Ensure that the secondary actuating rod is not restricting movement; bend the secondary closing tang if necessary then readjust it after pump adjustment. Place the pump rod in the inner hole in the lever. Measure from the top of the choke valve wall (next to the vent stack) to the top of the pump stem. If necessary, adjust to obtain the specified dimension by bending the lever while supporting it with a screwdriver. Adjust the idle speed.

Lightly open the primary throttle lever until the link just contacts the tang on the secondary lever. If necessary, bend the tang on the secondary lever to position the link in the center of the secondary lever slot.

Hold the choke valve closed, using a rubber band to keep it in place. Then, hold the vacuum break against the stop and measure the gap between the choke valve's lower edge and the main body. If necessary, adjust to obtain the specified gap by bending the vacuum break link.

When a carburetor develops faults after considerable mileage, it's often more cost-effective to replace the entire unit than to disassemble and replace individual components. However, if you choose to proceed with the rebuilding process, start by obtaining a repair kit containing the necessary gaskets and components, then follow these steps: Bend back the lockwasher tabs and remove the idle stop solenoid, followed by the larger idle stop solenoid bracket screw from the float bowl. Remove the clip from the upper end of the choke rod, disconnect the rod from the upper choke shaft lever, and remove it from the lower lever in the bowl. Drive the pump lever pivot inwards to remove the roll pin and detach the pump lever from the air horn and pump rod. Remove various screws retaining the air horn to the float bowl and the vacuum break hose, as well as the diaphragm unit from the bracket. Disconnect the choke assist spring and remove the metering rod hanger and secondary rods. Lift off the air horn, leaving the gasket in place, without attempting to remove air bleed or accelerating well tubes. If replacing the choke valve, measure it and the shaft. Do not remove the air valves and air valve shaft. Remove the pump plunger, air horn gasket, pump return spring, plastic filler over the float valve, and the power piston, noting the plastic retainer. Take out the metering rods from the power piston, followed by the float assembly, pull clip, fuel inlet needle, and needle seat. Unscrew the primary metering jets but avoid disturbing the secondary metering jets. Remove the discharge ball retainer and check ball, the baffle from the secondary side of the bowl, and the choke assembly, fast idle cam, intermediate choke rod, actuating lever, fuel inlet filter components, throttle body to bowl screws, throttle body, and throttle body to bowl insulator gaskets. Extract the pump rod from the throttle lever by rotation. It's not advisable to further disassemble, but if necessary, remove the idle mixture needles, pry out the plastic limiter caps, count the turns, and install replacements in the same position. Use new limiter caps after running adjustments. Clean all metal parts in a cold solvent, avoiding rubber parts, plastic components, the vacuum break assembly, or idle stop solenoid to prevent permanent damage. Blow clean, dry compressed air through the jets and inspect all parts for damage or wear, replacing as needed, and discard gaskets and the fuel inlet filter. Assembly is essentially the reverse of removal, with specific considerations, including idle mixture screw installation, float adjustment, air horn screw tightening sequence, pump lever attachment, and thorough post-reassembly settings and adjustments as previously outlined.

Seat the vacuum break diaphragm for pre-1972 models and check that the specified clearance exists between the dashpot and the end of the slot in the air valve lever, when the air valve is fully closed. If adjustment is necessary, bend the rod at the air valve end. For 1972 models onward, seat the choke vacuum break diaphragm using an outside source of suction, then measure the dimension between the end of the slot in the vacuum break plunger lever and the air valve when the air valve is fully closed. If adjustment is necessary, bend the rod at the air valve end.

Initially follow the procedure of 1 thru 3, but additionally plug the bleed hose in the end cover of the vacuum break unit using adhesive tape. Push up on the choke coil lever inside the choke housing towards the closed choke position. With the choke rod in the bottom of the slot in the choke lever, measure between the upper edge of the choke valve and the air horn wall. If necessary, bend the vacuum break rod at the point shown to obtain the specified dimension. On completion, remove the adhesive tape and install the vacuum hose. For the 454 engine, loosen the thermostatic cover screws and remove the cover and coil from the choke housing. Place the cam follower lever on the highest step of the fast idle cam. Seat the rear vacuum diaphragm using an external vacuum source (mouth or hand pump). Push up on the choke coil lever inside the choke housing (towards closed choke) until the step is pulled out and seated with the spring compressed. With the choke rod in bottom of the slot in the choke lever, measure between the upper edge of the choke valve plate and the air horn wall. The dimensions should be as specified at the beginning. Where necessary, bend the vacuum break rod at the point indicated. Remake the original vacuum hose connection and install the coil assembly and cover.

Remove the air cleaner then unscrew the fuel level sight plugs. Start the engine and allow it to idle. With the vehicle on a level surface the fuel level should be within ± 1/32 inch of the threads at the bottom of the sight plug port. If adjustment is required, loosen the inlet needle lockscrew and turn the adjusting nut clockwise to lower, or counterclockwise to raise, the fuel level. Tighten the lockscrew afterwards. (1/6 turn of the nut gives approximately m inch fuel level change). Allow approximately one minute for the fuel level to stabilize, then re-check. To ensure a proper secondary float level setting, open the primary throttles slightly, and hand operate the secondary throttles. Install the sight plug and air cleaner on completion.

First, unscrew the idle speed screw. Then, close both throttle valve plates completely and measure from the top surface of the air horn ring to the top of the pump rod. Finally, bend the rod to obtain the specified dimension.

Remove the front vacuum break diaphragm unit and the air valve dashpot rod. Using a suitable hexagonal wrench loosen the lock screw then turn the tension adjusting screw counterclockwise until the air valve is partly open. Hold the air valve closed then turn the tension adjusting screw clockwise the specified number of turns after the spring contacts the pin (Air Valve Spring Wind-up, Specifications). Tighten the lockscrew and install the air valve dashpot rod, and the front vacuum break diaphragm unit and bracket.

In 1978 General Motors changed the design of the carburetor idle mixture screw so that backing out the screw will not appreciably richen the mixture. Idle mixture adjustment is carried out with special propane enrichment equipment, a procedure best left to a dealer. For 1975 thru 1977, have the engine at normal operating temperature, air cleaner in position and air conditioning off. Connect a reliable tachometer to the engine. Disconnect the fuel tank hose from the vapor canister. Disconnect the lead from the idle stop solenoid. With automatic in Drive or manual in Neutral, turn the idle speed screw to obtain the curb (final) idle speed. Reconnect the solenoid. Crack open the throttle slightly to extend the solenoid plunger. Now turn the solenoid plunger screw to set the curb (initial) idle speed. Remove the tachometer and reconnect the fuel tank hose. The idle mixture screws are pre-set and fitted with limiter caps which allow them to be turned about one turn lean to rectify uneven idling. If after carburetor overhaul or replacement of components, the mixture must be adjusted beyond the limit of travel of the caps, carry out the following operations: Repeat the procedure. Break off the cap on the mixture screws. Set the idle speed to the curb (initial) figure using the solenoid plunger. Unscrew each of the mixture screws equally until the highest idle speed is achieved. Reduce the speed if necessary to curb (initial) 4 specifications using the solenoid plunger. Now screw in each of the mixture screws equally until the curb (final) idle speed is obtained. Reconnect the fuel tank hose and switch off the engine.

For 1969 models, the engine must be fully warmed up, ignition timing and dwell angle set correctly, and emission control systems functioning. An external tachometer is used, and the idle mixture screw(s) are adjusted for the highest steady idle speed. For 1970 models, distributor vacuum and fuel tank lines are disconnected and mixture screws backed out four turns, followed by adjusting the idle speed. 1971 models require adjusting the idle speed based on transmission and air conditioning status, with preset idle mixture screws. 1972 models have similar operations but adjust the idle stop solenoid screw differently with or without air conditioning. For 1973 and 1974 models, the idle stop solenoid screw is adjusted first, then the idle cam screw, and vacuum and fuel tank lines are reconnected. The idle mixture adjustment method for 1971 and later models involves breaking limiter caps, setting initial idle speed, adjusting mixture screws for maximum idle speed, and finalizing the idle speed as per specifications, then reconnecting hoses and fitting new limiter caps. An alternative method is using a CO meter to adjust the mixture screws based on CO levels within specified limits for smooth idling.

Connect a tachometer to the engine and then as a basic starting point, seat the idle mixture screws gently and then unscrew them three complete turns. With the engine at normal operating temperature, turn the idle speed screw until the specified idle speed is obtained with manual transmission in Neutral or automatic in Drive. Check the vehicle Decal for instructions whether the air conditioning system should be on or off. Adjust the idle mixture screws to obtain the highest idle speed. On vehicles fitted with an idle solenoid adjust the idle speed to 600 rpm by turning the solenoid hexagon headed screw. Disconnect the lead from the solenoid and check the idle speed. Now adjust the idle speed screw as necessary to obtain 400 rpm. With or without a solenoid fitted, adjust the mixture screw inwards to give a 20 rpm drop in engine speed (lean roll). Unscrew the mixture screw 1/4 of a turn. Repeat the operations described for the second mixture screw (where fitted). Readjust the idle speed screw if necessary to obtain the specified idle speed.

The following adjustment will normally only be required after overhaul or repair of the carburetor. Turn the idle stop screw in until it just touches the bottom step of the fast idle cam, then screw it in exactly one full turn. Position the idle screw so that it is on the second stop of the fast idle cam against the shoulder of the high step. Hold the choke valve plate towards the closed position (using a rubber band to keep it in place) and check the gap between the upper edge of the choke valve plate and the inside wall of the air horn. Adjust to the specified gap, if necessary, by bending the tang on the upper choke lever. The setting should provide the specified fast idle speeds.

Hold the throttle valve plates in the fully open position. At the same time, hold the choke valve plate towards the closed position using a rubber band to keep it in place. It is important to check the gap between the upper edge of the choke valve plate and the inside wall of the air horn. To adjust the gap to the specified value, bend the tang on the throttle lever.

Instead, it advises checking the carburetor number and consulting a partsman to ensure proper compatibility and avoid unauthorized modifications. All units feature automatic chokes, either hot air or electrically heated. Carburetor types vary based on engine capacity, ranging from dual to four-barrel downdraft designs. The Rochester 2G series is a dual-barrel, side bowl carburetor with fixed main metering jets calibrated through air bleeds and a power enrichment valve assembly. Some models incorporate an electric throttle closing solenoid for preventing dieseling. The choke operates via an exhaust manifold heated coil. The Rochester 4MV (Quadrajet) and M4MC (Quadrajet) series are downdraft two-stage units, with the former having primary and secondary sides and a common float chamber. Lastly, the Holley 4150 series, a 4-barrel carburetor, is used in early high-performance vehicles and features a center inlet with a temperature-sensing choke coil on the intake manifold.

Remove the air cleaner. Disconnect the fuel and vacuum pipes from the carburetor. Disconnect the choke rod or electrical wire (M4ME and M2ME carburetors). Disconnect the accelerator linkage. Disconnect the throttle valve linkage or downshift cable (automatic transmission). Remove all hoses and electrical connections, making very careful note of where they were removed from. Tags or coded pieces of tape will help. Remove the carburetor attaching nuts or bolts. Lift away the carburetor. Remove the gasket or insulator. Installation is the reverse of the removal procedure, but the following points should be noted: By filling the carburetor bowl with fuel, the initial start-up will be easier and less drain on the battery will occur. New gaskets should be used. Idle speed and mixture settings should be checked, and adjusted if necessary.

When a carburetor exhibits issues after substantial use, it is often more cost-effective to replace the entire unit rather than undergo complete disassembly and individual component replacement. However, in cases where disassembly and rebuilding are chosen, begin by obtaining a repair kit containing essential gaskets and parts. Follow this sequential process: Remove the wide-open throttle and idle solenoid along with the bracket assembly by unscrewing the retaining screws on the float bowl; avoid submerging these parts in carburetor cleaner. Proceed to remove the upper choke lever by loosening the retaining screw and rotating the lever. Extract the choke rod from the lower lever within the float bowl casting by holding the lever outward and counterclockwise twisting the rod. Using a drift, drive the pump lever pivot pin inward to facilitate the removal of the lever, while noting the position of the accelerator pump rod. Remove the pump lever from the pump rod. Disconnect the vacuum break hose from the tube on the float bowl. Next, remove the nine air horn attaching screws, with two being countersunk in the carburetor's center, and lift the air horn vertically off the float bowl. From the air horn assembly, remove the vacuum break control with its bracket. Remove the pump plunger stem seal by inverting the air horn and removing the staking; discard the retainer and seal. The air horn assembly comprises an idle air bleed valve preset at the factory, so it should not be removed unless replacement is necessary, and it should not be cleaned traditionally to avoid damaging the O-rings sealing the idle air bleed valve. While depressing the pump plunger stem, lift the corner of the air horn gasket attached to the float bowl to remove the pump plunger from its well. Remove the solenoid metering rod plunger by lifting it straight up. Remove the rubber seal surrounding the mixture control solenoid plunger. Take out the air horn gasket from the float bowl. Remove the pump return spring from the well. Extract each metering rod assembly carefully from the float bowl, ensuring the return spring is included. Remove the mixture control solenoid from the float bowl by removing the two attaching screws; do not remove the solenoid connector. Turn the mixture control screw counterclockwise, remove it, and then carefully lift the solenoid and connector assembly from the float bowl. Remove the plastic insert from the cavity under the solenoid connector in the float bowl. Remove the solenoid screw tension spring near the float hanger clip. Lift out the float assembly and float needle by pulling up on the retaining clip, and remove the needle and seat. Extract the large mixture control solenoid spring from the bottom of the float bowl. Remove the main metering jets if required. Remove the pump discharge check ball retainer and check ball, and the pump well fill slot baffle if needed for replacement. Remove the rear vacuum break control with its attaching bracket; avoid submerging this in carburetor cleaner. The non-adjustable choke is typically intended as a permanent fixture and may require specific overhaul instructions; disassembly involving rivet removal may be necessary. Remove the fuel inlet nut, gasket, check valve filter assembly, and spring from the float bowl. Undo the four throttle body attaching screws to remove the throttle body assembly. Extract the pump rod from the throttle lever by rotating the rod until the tang aligns with the slot in the lever. Unless replacement is necessary, avoid removing the plugs covering the idle mixture needles, which is uncommon in a standard overhaul. Clean all metal parts in a suitable cold solvent, excluding rubber parts, plastic parts, the vacuum break assembly, wide-open throttle switch, solenoid, or air horn assembly. Do not probe the jets; instead, clean them with clean, dry compressed air. Inspect all fixed and moving parts for cracks, distortion, wear, and other damage, replacing components as needed. Discard all gaskets and the fuel filter. Assembly is generally the reverse of the removal process, but consider these points: To adjust the float level, hold the float retaining clip firmly and lightly push down on the float arm. Measure from the top of the float bowl casting (without gasket) to the top of the float about ⅛" back from the toe, and adjust the float arm as necessary. Tighten the nine air horn attaching screws securely in the specified sequence.

Hold the throttle lever wide open (using a rubber band to keep it in place). Hold the choke valve towards the closed position against the unloader tang of the throttle shaft. Measure the gap between the choke valve lower edge and main body. Adjust, if necessary, to obtain the specified gap by bending the choke rod at the offset bend.

Place the idle speed screw on the highest step of the fast idle cam. Then, loosen the choke coil cover retaining screws. Rotate the cover against the coil tension until the choke begins to close. Continue rotating until the index mark aligns with the specified point on the choke housing, which is between the center and 1/2 notch lean. Finally, tighten the choke cover retaining screws.

Using an external source of suction, seat the front vacuum break diaphragm. Suction from the mouth or a small hand pump is normally adequate. Ensure that the air valves are completely closed then measure between the air valve dashpot and the end of the slot in the air valve lever. This dimension should be 0.015 in. Bend the air valve dashpot rod at the point shown, if adjustment is necessary.

In 1969 models, connect a tachometer and adjust the idle mixture screws, then set the idle speed screw to specifications. Follow vehicle Decal instructions regarding the air conditioning system. Adjust idle mixture screws for maximum idle speed, fine-tune with or without an idle solenoid, and perform a lean roll adjustment. In 1970 models with 350 and 400 cu in engines, adjust the idle speed screw, unscrew mixture screws, and adjust them for specified engine speeds. For 1970 models with a 454 cu in engine and automatic transmission, adjust the idle speed and mixture screws. In 1970 models with a 454 cu in engine and manual transmission, perform adjustments to achieve specified engine speeds and perform lean drop adjustments. For 1971 and 1972 models with 350, 402, and 454 cu in engines, follow a step-by-step procedure involving the idle stop solenoid screw, fast idle adjustment, and mixture screw adjustments. In 1973 and 1974 models with 350, 400, and 454 cu in engines, similar operations are conducted, referencing specifications for initial, final, and fast idle settings.

Hold the choke valve closed then pull down on the coil rod to the end of its travel. The rod should contact the bracket surface. Bend the choke coil rod, if necessary, so that the top of the rod aligns with the bottom of the holes. Connect the coil rod to the choke lever and install the retaining clip. Check that the choke operates freely over its full range of travel. For 1972 models onwards, rotate the choke coil lever counterclockwise to fully close the choke. With the coil rod disconnected and the cover removed, push down on the rod until it contacts the bracket surface. The coil rod must fit in the choke lever notch; bend the rod to adjust if necessary. Install the choke coil cover. Install the coil rod in the choke coil lever slot and install the retaining clip. Check that the choke operates freely over its full range of travel.

Open the throttle slightly then close the choke plate, positioning the fast idle lever against the top step of the fast idle cam. Adjust the fast idle to give the specified throttle opening on the idle transfer side of the carburetor. If necessary, make adjustments by bending the fast idle lever.

Place the idle speed screw on the second step of the cam, against the high step. Check the dimension between the upper edge of the choke valve and the air horn wall. If adjustment is necessary to obtain the specified dimension, bend the choke lever tang.

Hold the choke valves and secondary lock-out valves closed then measure the clearance between the lock-out pin and lock-out lever. If adjustment is necessary, bend the lock-out pin to obtain the specified clearance (0.015 inch). Push down on the tail of the fast idle cam to hold the choke wide open. Hold the secondary throttle valve partly open then measure between the end of the lock-out pin and the toe of the lock-out lever. This should be 0.015 inch. If adjustment is necessary, file the end of the lock-out pin but ensure that no burrs remain afterwards.

Adjust the choke coil, as previously described. Hold the throttle valves wide open and the chokes fully closed. A rubber band can be used on the tang of the intermediate choke lever if the engine is warm. Measure between the upper edge of the choke valve and the air horn wall. If adjustment is necessary, bend the tang on the fast idle lever to obtain the specified dimension. Ensure that the tang on the fast idle cam lever contacts the center point of the fast idle cam after adjustment.

The carburetor/TBI is attached to the top of the intake manifold by four nuts or bolts. These fasteners can sometimes work loose from vibration and temperature changes during normal engine operation, causing a vacuum leak. To properly tighten the mounting nuts/bolts, a torque wrench is necessary. If you do not own one, they can usually be rented on a daily basis. Remove the air cleaner assembly, tagging each hose to be disconnected with a piece of numbered tape to make reassembly easier. Locate the mounting nuts/bolts at the base of the carburetor/TBI. Decide what special tools or adapters will be necessary, if any, to tighten the fasteners with a socket and the torque wrench. A torque check of the carburetor or fuel injection unit mounting bolts will help eliminate vacuum leaks in the induction system. Tighten the nuts/bolts to the specified torque. Do not overtighten them, as the threads could strip. If you suspect that a vacuum leak exists at the bottom of the carburetor/TBI, obtain a length of hose about the diameter of fuel hose. Start the engine and place one end of the hose next to your ear as you probe around the base with the other end. You will hear a hissing sound if a leak exists. If, after the nuts/bolts are properly tightened, a vacuum leak still exists, the carburetor/TBI must be removed and a new gasket installed. After tightening the fasteners, reinstall the air cleaner and return all hoses to their original positions.