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.

To start, loosen the adjustment screw until the throttle plates completely close. Adjust the screw to slightly touch the throttle lever and turn it another half twist. First, you must slacken the adjusting screw so that the throttle plate will be in its fully closed position. After that, rotate this adjusting screw to meet with a throttle lever at an extra half a spin.

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.

The throttle lever was held wide open, with a rubber band to maintain that position, and then the pump lever was fully compressed. The distance between the spring adjusting nut and pump lever arm should be measured. In case of need, adjust so that the gap is 0.015 inch by turning the nut/screw with prevention of the opposite end moving. Thereafter shut off the throttle lever before opening it partially again. If the operating lever has moved slightly, then one will know that the pump tip-in is correct.

If it is an electrical heated choke, then make sure that the coil tang touches the bottom side of the inner face of the arm of the choke coil lever pickup. Thereafter, put the fast idle cam follower onto the high step of the cam. Then, turn the cover and coil assembly counterclockwise until the choke valve just closes. Lastly center index marks and install cover and screws. It's good to note that ground contact for an electrically heated choke is through a metal plate at the rear of a choke assembly. Don't put a gasket between the cover and housing as this will break the circuit.

Whenever a carburetor gets faulty after long usage time, it is often cheaper to replace the entire unit than replacing individual components. But if you decide to proceed with the rebuilding process, get a repair kit that has all the required gaskets and parts and then follow these steps: in the beginning, loosen up fuel inlet fitting, sight plugs of fuel bowl and needle as well as seat lockscrews. Disconnect secondary throttle operating rod, throttle operating assembly and gasket, primary/secondary fuel bowls metering bodies associated gaskets. Disconnect hose at vacuum break them remove throttle body to main body screws and gasket. Loosen inlet needle and seat lock screw followed by removing the needle and seat assembly. Remove hinge pin retainer then float slides out accompanied by spring if necessary. Inlet fitting, fuel filter with spring are removed with the sight plug and gasket before gaskets are removed also from this area. From primary bowl remove air valve assemblies (if applicable) pump diaphragm parts main metering jets power valves idle mixture screws seals. The diaphragm cover disassembles secondary throttle operating assembly including spring diaphragm.Disconnecting link at choke lever removes vacuum break retaining screws along with assembly .Choke lever retaining clip lever fast idle cam needes to be taken off.Remove pump discharge nozzle parts discharge check valve further dismantling file away staked ends of shaft screws take out shafts choke rod seal included with them.Throttle body parts: including pump operating lever assembly spring bolt nut idle speed screw secondary throttle shaft diaphragm lever primary throttle shaft fast idle cam lever key secondary locknut throttle connecting link from these shaft levers.File away staked ends of attaching screws for throttle plate take out screws plates withdraw shafts from flange.Remove accelerator pump cam vacuum break hose through which throttle lever passes.Clean all metallic pieces in a suitable cold solvent avoiding non-metallic or rubber plastic components.Do not probe jets blow them out with clean dry compressed air. Study all the parts for replacement if they are damaged, worn out, cracked or distorted and discard the gaskets.Check the secondary throttle operating diaphragm's operations.Assembly is essentially opposite of disassembly with specific considerations given to throttle shaft bushings, idle speed screw adjustment that should be done when throttle valves are oriented choke valve free movement and proper installation of idle mixtures screws with new seals.Ensure accurate float adjustment secondary throttle stop valve fast idle cam accelerator pump choke unloader vacuum break adjustments as needed.

Replacing the whole unit of a carburetor that has become faulty after long use is often cheaper than taking it apart and replacing all its components. However, if one decides to take it apart and rebuild it, start by having a repair kit that contains essential gaskets and parts. Here is a process of stripping the carburetor down: To begin with, bend back lockwasher tabs then remove idle stop solenoid if so equipped. Then, 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, then unscrew two retaining screws to remove the diaphragm from air horn. After removing fuel inlet filter nut, filter, spring and two gaskets; remove pump rod from throttle lever after taking off retaining clip. Rotate upper pump lever counterclockwise and remove pump rod from lever. Remove fast idle cam and its retaining screw while holding choke open and remove choke rod from upper choke lever. Continue by removing air horn using eight screws at float bowl including removal of float hinge pin, float, splash shield, and float needle. Unscrew float needle seat with gasket followed by removal of air horn to float bowl gasket. Depress power piston shaft to eject piston from casting with help of spring. Remove inner pump lever retaining screw and outer pump lever as well as plastic washer from air horn putting plunger in gasoline so that rubber does not dry out. If choke valve or shaft is being replaced locate two staked screws that hold them in place then lift valve out along with shaft and lever out of air horn assembly. Remove pump plunger return spring from pump well if applicable followed by inlet check ball where applicable plus pump inlet screen located on bottom of float bowl where applicable also mentioned earlier main jets as well as power valve and gaskets could be unscrewed and cluster plus gasket removed using three screws and washers with attention to fiber washer on center one. Remove pump discharge spring retainer, the spring, and the check ball. Lastly, remove throttle body to bowl attaching screws; then take off body and gasket. It is not advised that further disintegration be done, however, in order to take out idle mixture needles pry plastic limiter caps out count number of turns required bottom all needles fit replacements at same position. Wash all metal parts in a suitable cold solvent except do not immerse rubber, plastic, vacuum break assembly or idle stop solenoid, blow clean jets with compressed air then examine all stationary and moving parts for cracks wear distortions or damages replacing as necessary discard all gaskets and fuel inlet filter. The reverse of removal is essentially the assembly process where there are certain points to note like idle mixture screws adjustment choke valve positioning float adjustments even tightening of air horn screws versus one another. Finally, perform all necessary settings and adjustments after reassembly.

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.

First off, turn the engine off and set the throttle on the fast idle cam's high step. Disengage and cap the EGR valve vacuum pipe. Likewise, disengage and plug distributor's vacuum hose. Start the engine while in 'Park' or 'Neutral' without stepping on the gas pedal. Adjust your fast idle speed screw to match the rpm on your emission Decal. Turn off the engine by opening up on the throttle in order to release it from its fast idle cam position. Lastly, re-plug all vacuum hoses at 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.

Keep the choke valve open while pulling down on the coil rod until it reaches the end of its travel for pre-1972 models. The top of the hole in the choke lever that it is sliding through should be even with the bottom of that hole. Adjust by bending at point indicated. Attach rod onto choke lever and secure with retaining clip. Ensure that choke moves freely. Open up fully the choke valve plate for 1972 models onwards. Detach thermostatic coil rod from upper lever, then depress the rod to its lowest level possible, downwards towards bottom side as much as feasible. The upper part of the rod should be in line with the lower end of a hole located in a choke lever. If required, adjust by bending 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.

Seat the vacuum break diaphragm via a different suction source like mouth or small hand pump. Mask the vacuum break bleed hole with a piece of masking tape. Set up the idle speed screw on the high step of the fast cam idle. Keep the choke coil lever inside the choke housing towards the closed choke position. Check out the distance from upper edge of choke valve to air horn wall. If necessary, bend vacuum break rod for adjustment to obtain this specified dimension. Remove masking tape from vacuum unit bleed hole and reattach it back to 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.

Start with the second step of the fast idle cam and place the cam follower against the high step. Then, with the help of the external lever, turn the choke valve in a clockwise direction to move it closer to its shut position. Note that this should be done following specification. Check that there is specified space between the edge of choke valve (on lever side) which is at bottom and air horn wall. Where necessary, adjust by bending the choke rod.

You have to remove both the three screws and retainers. Detach the cover of the thermostatic coil gasket as well as the inside baffle plate assembly. While placing idle speed screw on fast idle cam's highest step, you must keep in mind that. The intermediate choke lever should be pushed up so that it closes the choke valve. The edge of a gauge must align with the edge of an inside choke housing's coil lever. Adjust by bending once every choke rod if need is interfered with.

If a carburetor develops faults after many miles of use, it is often cheaper to replace the whole unit rather than replacing individual components. However, if you decide to strip and rebuild the unit, start by getting a repair kit containing the necessary gaskets and components, and follow these steps: Remove idle stop solenoid and bracket assembly from carburetor if it has one by unfastening securing screws. Unscrew one screw to remove the upper choke lever, rotate it for removal, and break it loose from the choke rod. Remove the choke rod from float bowl through lower lever by prying lever outward with small screwdriver while twisting rod counterclockwise. Take out vacuum hose from the front vacuum break unit. Remove the metering rod hanger small screw then pull out secondary metering rods and hanger. Use proper drift punch to drive small pump lever pivot roll pin inward for easy removal of lever. Remove float bowl by taking off 2 long screws, 5 short screws, 2 countersunk head air horn screws without detaching gasket. Never take out those little tubes sticking up from air horn. Pull off front vacuum break bracket; disconnect air valve dashpot rod from diaphragm assembly and air valve lever lift upunit . If needed, remove staked choke valve attaching screws before pulling out choke valve or shaft from air horn without disturbing the air valve or air valve shaft. Remove float bowl gasket being careful not to distort springs holding main metering rods.; take out pump plunger and pump return spring from pump well.Squeeze down on power piston stem releasing it allowing metering rods to slide free along with power piston spring coming out of well.Remove tension springs connecting metering rods to power piston; turn rods to release them.Carefully remove plastic filler block above float valve then pull float assembly down removing needle.Remove needle seat and gasket; unscrew cover screws carefully lifting out metering rod with filler spool from float bowl. Remember that the adjustable part-throttle (APT) metering rod assembly should not be messed with.Remove primary main metering jets and pump discharge check ball retainer as well as pump discharge check ball.Remove rear vacuum break hose and bracket retaining screws; pull back vacuum break rod out of slot in plunger head.Depress fast idle cam to remove vacuum break rod, disengage it from hole in intermediate lever, unscrew choke cover attaching screws and retainers and lift off cover and gasket.Remove choke housing assembly from float bowl by removing retaining screw and washer, secondary throttle valve lock-out lever, lower choke lever by inverting float bowl, plastic tube seal from choke housing, intermediate choke shaft if required followed by fast idle cam when applicable.Remove fuel inlet filter nut, gasket and filter from float bowl; remove pump well fill slot baffle and secondary air baffle if used.Release throttle body attaching screws; detach float bowl then remove insulator gasket.Pull pump rod out of lever on throttle body. If idle mixture needles must be removed, pry plastic limiter caps out of the way count the number of turns necessary for bottoms-out orifice plugs replace them at same location.New limiters should be installed after set-up.Flush all metal parts using a suitable cold solvent except rubber parts, plastic components or aneroids, pump plungers or filler spools or aneroids or vacuum breaks.Evaporate cleaner through them instead touching jets; avoid use of probes.Visually inspect all parts for damage, wear cracks distortion etc., replacing ones having defects and discard gaskets including fuel inlet filter.The normal method is to reassemble everything in reverse order but several important points must be remembered: With new idle mixture screws where the original setting is unknown seat them 4 full turns back from bottom. Use correct orientation of plastic insert cup seals, proper assembly of choke components, accurate float adjustment, and tight air horn screw sequence. After the entire unit is put back together, check if the front and rear vacuum breaks, fast idle cam, choke coil lever, and automatic choke coil are adjusted right. Replace the APT metering rod only if there is damage or failure of aneroid; following prescribed procedures for precision fitments.

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.

Usually, when a carburetor has problems after long time usage, it is cheaper to replace the entire unit than trying to completely disassemble and replace all part. Nevertheless, if one chooses to dismantle and rebuild the carburetor for some reasons. You should follow these steps: If the solenoid in a carburetor (which pertains either automatic transmission or air conditioning) is present then remove it by bending back lockwasher tabs and unscrewing the large nut holding the solenoid onto its bracket while avoiding dipping into solvents. Then proceed to remove the fuel inlet filter components, disconnecting the lower end of the pump rod from throttle lever as well as removing the upper end of pump rod from pump lever. Disconnect vacuum break diaphragm hose and remove diaphragm assembly with vacuum break lever from choke shaft's end; intermediate choke rod located on coil housing is also removed. After that remove fast idle cam with its retaining screw and lift off air horn by removing eight attaching screws and lockwashers. Take out float hinge pin, float, float needle and pull clip where applicable. Unscrew float needle seat and take out gasket. Press down power piston to free it then remove pump plunger assembly together with inner pump lever by loosening set screws. In case overhaul of pump assembly is necessary then snap off flattened end of plunger stem on pump plunger.Remove outer lever, shaft assembly plus plastic washer from plunger shaft for making sure they are left on top of air horn gasket plus fuel inlet baffle respectively.Be careful not only when taking off choke valve but also dressing up screws for removal use may be required as well as choke valve shaft.Extract fast idle cam rod/lever through same.Disengage pump plunger return spring followed by turning bolt over before sliding aluminum ball out.Screw out main metering jets along with their power valves removing gaskets before unscrewing venturi cluster using three screws and gasket.Remove pump discharge spring retainer, spring and check ball from discharge passage.Take out three large throttle body to bowl attaching screws and lockwashers so that the throttle body together with its gasket is removed.Peel off thermostatic choke coil cover/gasket while avoiding removal of cap baffle under coil cover also remove choke housing baffle plate.From inside choke housing, remove attaching screws, housing as well as gasket. Remove screw at end of intermediate choke shaft then take off choke lever together with inner choke coil lever/shaft assembly plus rubber dust seal.Further disassembly particularly to do with throttle valves/ shafts is not recommended because it may complicate their re-assembly.Occasionally, idle mixture needles have to be removed by breaking plastic limiter caps and noting the number of turns required to bottom needles for replacements.Limiter caps should be new in case running adjustments are done.Rinse all metal parts in suitable cold solvents, making sure that they are not soaked into rubbers or plastics including diaphragm assemblies and pump plungers which could lead to permanent damage.Always blow through jets instead of probing them by use of clean dry compressed air.Inspect all fixed/moving parts for cracks/distortion/wear/damage so as to replace them where necessary.Discard all gaskets except the fuel inlet filter. Assembling is basically a reverse of removing; but, the following are specific pointers to note: installation of new idle mixture screws; proper rubber dust seal orientation in choke housing cavity; positioning of choke valve, float level and float drop checks; correct assembly of venturi cluster; tightening air horn screws as specified for 2GV carburetors. After reassembly, make necessary settings and adjustments.

After a carburetor has been used for some time, it is often more cost-effective to replace the complete unit than to disassemble and replace certain parts. However, if one chooses to take apart and rebuild the carburetor, he or she should start by acquiring a repair kit with required gaskets and parts. To do this, remove the solenoid (if installed) from the float bowl; unscrewing of the solenoid and bracket assembly screws would be necessary while avoiding any dip in carburetor cleaner. Take off the choke lever at the top of the carburetor by removing its retaining screw and turning it until it releases the choke rod. Unscrew choke rod from lower lever while twisting counter-clockwise as lower lever is held outwards. Observe where accelerator pump rod contacts on its lever is located then push pivot pin through slightly in order to remove pump lever. Remove seven bolts fastening upper air horn assembly to bowl, lifting air horn straight up off float bowl. From air horn assembly, take out vacuum break hose and vacuum break control with bracket assembly. Lift air horn gasket off top of float bowl assembly taking care not distort spring that holds main metering rods in place.Remove pump plunger from pump well followed by plunger return spring.Remove power piston/metering rods from well by depressing/releasing piston allowing it snap free.Remove metering rods from power piston by unhooking spring from each rod then rotate rod to get out of hanger.Remove plastic filler block over float valve then remove float assembly, float needle/retaining pin/seat/gasket.Remove main metering jets if necessary also pump discharge check ball retainer/check ball & pump well fill slot baffle.The choke cover held in place by rivets is removed when drilling out rivet heads.Eliminate the choke retainers release gasket cover along with choke cover itself avoid removal of baffle beneath coil surrounding the choke cover.Choke housing comes out of the float bowl after unscrewing bolt inside the housing.Remove rear vacuum break rod from intermediate choke lever.Take out retaining screw for choke coil lever and then remove it from shaft to get the intermediate choke shaft.Slide out intermediate shaft this will help you remove fast idle cam from shaft.Remove cup seal from float bowl insert without removing insert itself.Turn float bowl over and take choke lever out of cavity.From float bowl assembly, remove fuel inlet nut/gasket/check valve filter/spring or.Getting loose screws which attach the throttle body with a float bowl separate pump rod with a throttle lever.Make sure not to take off plugs that cover idle mixture needles unless necessary to replace mixture screws; clean mixture passages instead.Wash all metallic parts in a suitable cold solvent, but do not put rubber parts, plastic parts, vacuum break assembly and idle stop solenoid into solvent.Do not press on jets; use dry compressed air only. Examine all parts of fixed and moving types for cracks, distortion, wear or damage, change components where necessary and discard the gaskets as well as the fuel inlet filter. Assembling is almost same as removing but it should be noted that choke coil cover assembly must be adjusted after inside coil lever adjustment, float level must be adjusted and air horn attaching screws to be tightened 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.

A sensitive approach is necessary to open the primary throttle lever. Turn it gently to crack a little, ensuring that the connecting link reaches the tang of the secondary lever. For correct operation of the throttle, this specific alignment is very important. Alignment problems can be fixed by repositioning the link so that it fits exactly in the middle of the slot on the secondary lever. If needed, bend carefully tang on secondary lever to help facilitate this adjustment with fitting of link perfectly for smooth operation of throttle.

Hold choke valve closed with rubber band. Then, hold vacuum break against stop and measure the gap between lower edge of choke valve and main body. If necessary, adjust by bending vacuum break link to get the specified gap.

If a carburetor develops problems after many miles, it is often more economical to buy a new one than to dismantle and replace the individual components. However, if you choose to proceed with the rebuilding process, start by obtaining a repair kit containing necessary gaskets and components. Then do this: Bend back the lockwasher tabs and remove the idle stop solenoid. After that, remove the larger idle stop solenoid bracket screw from the float bowl. Remove the clip from the upper end of the choke rod. Disconnect this rod from the upper choke shaft lever and take away it from lower lever in bowl. Drive pump lever pivot inward to remove roll pin and release pump lever from air horn/pump rod. Take out screws holding air horn to float bowl and vacuum break hose, also lift diaphragm unit off bracket. Disconnect choke assist spring and remove metering rod hanger/secondary rods. Lift off air horn leaving gasket in place without trying to remove air bleed or accelerating well tubes etc. If replacing choke valve, measure it along with shaft. Do not touch air valves or air valve shafts at all! Remove pump plunger; (also) air horn gasket; (also) pump return spring; plastic filler over float valve; power piston with plastic retainer; metering rods held by power piston; float assembly separated by pull clip; fuel inlet needle that seats into needle seat (plastic). Unscrew primary metering jets but don't touch secondary metering jets inside hollow tube section of casting area on top of float bowl for discharge ball retainer or check ball bottom side of bowl where it is retained as well as choke assembly/fast idle cam/intermediate choke rod/vacuum break hoses/actuating levers/fuel inlet filter components/throttle body/bowl screws holding throttle body/bowl insulator gaskets between them both i.e., bolts attaching these separate parts altogether. Extract pump rod from throttle lever by rotation. It is not recommended to disassemble further but if necessary, remove idle mixture needles and pry out plastic limiter caps etc., count the turns, and put the replacements back into same position. New limiter caps should be used when running adjustments. Allowing cold solvent to touch rubber parts, plastic components, vacuum break assembly or idle stop solenoid would be damage. Jets should then be blown clean dry compressed air and all parts examined for wear or damage as required with gaskets and fuel inlet filter thrown away Assembly is essentially the reverse of removal and there are some considerations to be made in this regard such as idle mixture screw installation, float adjustment, sequence of tightening air horn screws, fitting pump lever and finally post-reassembly settings with thorough checks as mentioned before.

To seat the vacuum break diaphragm for pre-1972 models, check that there is specified clearance between dashpot and end of slot in air valve lever when air valve is fully closed. If adjustment is needed, bend rod at air valve end. For 1972 models and beyond, produce a vacuum on the outside of the choke vacuum break diaphragm and then measure the distance from the end of the slot in the vacuum break plunger lever to the air valve with it closed completely. 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.

The engine must be fully warmed up for 1969 models, the ignition timing and dwell angle must be set correctly, and the emission control systems must function. An external tachometer is used while the idle mixture screw(s) are adjusted to get the highest steady idle speed. For 1970 models, distributor vacuum lines, fuel tank lines are disconnected and mixture screws backed out four turns and then adjust the idle speed. These include adjusting only for transmission or air conditioning status depending on each other and having preset idle mixture screws for each. With or without air conditioning, 1972 models do similar operations except they have a different way of adjusting the idle stop solenoid screw. The first one to be adjusted is the idle stop solenoid screw on 1973 and 1974 models followed by reconnecting vacuum lines and fuel tank lines in that order, then recalibrating the idle cam screw. In breaking limiter caps, setting initial idle speed, adjusting mixture screws for maximum idle speed, finalizing the idle speed as per specifications, then reconnecting hoses and fitting new limiter caps will involve removing all limiter caps. The alternative method could use CO meter to adjust the mixture screws within specified limits of CO levels at 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 next time you overhaul or repair the carburetor, you may need to make the following adjustment. Turn in the idle stop screw until it touches just the bottom step of fast-idle cam, then turn it in one full turn. Positioning the idle screw so that it rests on the shoulder of the high step of fast idle cam's second stop. Hold choke valve plate towards its closed position by use of a rubber band and check clearance between top edge of choke valve plate and inside wall of air horn. The specified clearance may be obtained by bending upper tang from choke lever if required. The setting should provide the desired fast idle speeds.

The throttle valve plates must be held in the fully open position. You can also hold the choke valve plate towards the close position by means of a rubber band tied across it. It is important to check if there is a gap between the top edge of the choke valve plate and the inner wall of the air horn. Adjusting this gap to specified value involves bending tang on throttle lever.

This advises people to cross-check their carburetor numbers and consult a partsman in order to be sure of correct compatibility and evade any alterations that are unauthorized. All units have automatic chokes-hot air or electrically heated. The type of carburetor changes depending on the size of the engine; it can be four-barrel downdraft or dual. The Rochester 2G series, a side bowl carburetor with fixed main metering jets calibrated through air bleeds and a power enrichment valve assembly, is a typical example of such system. Some models include an electric throttle closing solenoid for preventing dieseling. It used an exhaust manifold heated coil to operate the choke. The Rochester 4MV (Quadrajet) and M4MC (Quadrajet) series are downdraft two-stage units, with the former having primary and secondary sides and common float chamber. Finally, Holley 4150 series is a four-barrel carburetor used in early high-performance vehicles which has a center inlet fitted with an intake manifold temperature sensing choke coil.

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 fast idle cam's highest stepping at the idle speed screw. Then, loosen the retaining screws for choke coil cover. Rotate the cover against tension of coil until choke begins to close. Continue rotation until index mark is aligned with indicated point on choke housing ranging between lean center and a notch past 1/2. Lastly, secure choke cover's retention screws tightly.

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.

To set idle mixture screws, connect a tachometer to 1969 models and then adjust them; then, check the idle speed screw against specifications. Follow the decal information on the vehicle concerning the air conditioning system. You can also make use of an idle solenoid, or without one you can fine-tune by adjusting idle mixture screws to obtain maximum idle speed and perform a lean roll adjustment. On 1970 models equipped with 350 and 400 cu in engines, adjust your idle speed screw and turn off mixture screws to set for specified engine speeds. Adjust the idle speed and mixture screws for a model with a 454 cu in engine and an automatic transmission made in 1970. For a model with manual transmission in 1970 using a 454 cu in engine, make adjustments to meet specified engine speeds, as well as lean drop adjustments. Involving the idle stop solenoid screw, fast idle adjustment back-off screw, and mixture screw adjustments procedure applied on models during years of 1971 and 1972 having engines with cubic capacity of 350, 402, or even that ranging up to 454 is followed stepwise. In similar operations conducted during years of 1973 or '74 on models having engines with cubic capacities of either 350-,400-,or454-inches,referencing specifications are provided for initial,fianl,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.

Adjust the fast idle so that there is a specific opening in the throttle valve on the carburetor's idle transfer side of it. In case of any necessity, correct the settings by bending the fast idle lever. Opening up the throttle a bit would be followed by closing of the choke plate while positioning the fast idle lever against top step of fast idle cam.

First of all, you should look for the dimensions by first finding the distance from the top edge of the choke valve to the air horn wall. If necessary, you have the option to bend down the choke lever tang in order to achieve this specific measurement. Also, it puts an idle speed screw at the second step of its cam which is opposite to the high step.

To measure the clearance between the lock-out pin and the lock-out lever, hold the choke valves and secondary lock-out valves closed. If necessary, bend the lock-out pin to achieve this clearance (0.015 inch). The choke should be held wide open by pushing down on the tail of the fast idle cam. Then measure from end of lockout pin to toe of l.o. lever; 0.015 inch. File but make sure that no burr remains on the end of l.o. pin when adjustments are needed.

As it has been described before, choke coil should be adjusted. The throttle valves have to be held wide open and the chokes kept completely closed. In case the engine is warm, a rubber band can be attached on the tang of the intermediate choke lever. Take a measurement between the upper edge of the choke valve and the air horn wall. If necessary, bend the tang on the fast idle lever to obtain this specified dimension. After adjustment, you should ensure that it contacts the center point of fast idle cam through making sure that tang on fast idle cam lever contacts are in order.

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.