See Figure 1
The 5.0L (VIN Y) engine uses the E4MC. This carburetor is of the downdraft design used in conjunction with the CCC system of fuel control. They have special design features for optimum air/fuel mixture control during all ranges of engine operation.
An electric solenoid in the carburetor controls the air/fuel ratio. The solenoid is connected to an Electronic Control Module (ECM) which is an on board computer. The ECM provides a controlling signal to the solenoid. The solenoid controls the metering rod(s) and an idle air bleed valve to closely control the air/fuel ratio throughout the operating range of the engine.
See Figure 2
General Motors Rochester carburetors are identified by their model code. The first number indicates the number of barrels, while one of the last letters indicates the type of choke used. These are V for the manifold mounted choke coil, C for the choke coil mounted in the carburetor body, and E for electric choke, also mounted on the carburetor. Model codes ending in A indicate an altitude-compensating carburetor.
Because of the intricate nature and computer controls, the E4M carburetors should only be serviced by a qualified technician.
The following should be observed before attempting any adjustments.
- Thoroughly warm the engine. If the engine is cold, be sure that it reaches operating temperature.
- Check the torque of all carburetor mounting nuts and assembly screws. Also check the intake manifold-to-cylinder head bolts. If air is leaking at any of these points, any attempts at adjustment will inevitably lead to frustration.
- Check the manifold heat control valve (if used) to be sure that it is free and not sticking closed.
- Check and adjust the choke as necessary.
- Adjust the idle speed and mixture. If the mixture screws are capped, don't adjust them unless all other causes of rough idle have been eliminated. If any adjustments are performed that might possibly change the idle speed or mixture, adjust the idle and mixture again when you are finished.
Before you make any carburetor adjustments, ensure the engine is in proper tune. Many problems which are thought to be carburetor related can be traced to an engine which is simply out-of-tune. Any trouble in these areas will have symptoms like those of carburetor problems.
See Figure 3
- Attach a rubber band to the vacuum break lever of the intermediate choke shaft.
- Open the throttle to allow the choke valve to close.
- Place an angle gauge set to specification on the choke valve.
- Place the fast idle cam "A" on the second step against the cam follower lever "B", with the lever contacting the rise of the High Step. If the lever does not contact the Cam, turn the fast idle adjusting screw "C" in additional turn(s).
- Adjust, if bubble is not recentered, by bending fast idle cam kick lever with a suitable tool.
See Figure 4
- Remove the air horn and gasket from the float bowl. Hold the float retainer down firmly. Push the float down (lightly) against the needle.
- Position a T-scale over the toe of the float 3 / 16 inch from the end of the float toe.
- If the float level varies more than 1 / 16 inch from the specified setting, it must be reset.
- Hold the float retainer in place.
- Push down on the center of the float until the correct level is obtained.
- Lift out the metering rods and remove the solenoid connector screws.
- Turn the lean mixture solenoid screw clockwise, counting and recording the number of turns required to seat the screw in the float bowl.
- Turn the screw counterclockwise and remove it. Lift the solenoid and the connector from the float bowl.
- Remove the float and bend the arm up to adjust. The float must be correctly aligned after adjustment.
- To install the components, reverse the order of removal. Back out the solenoid mixture screw the number of turns that were recorded in step 2.
Due to the design of the throttle cable for the carburetor systems, no adjustments of the throttle linkage can be made.Choke Unloader (Primary)
See Figures 5 and 6
- Connect a rubber band to the green tang of the intermediate choke shaft.
- Open the throttle to allow the choke valve to close.
- Set up the angle gauge and set to specifications.
- Using a vacuum source, retract the vacuum break plunger. The air valve rod must not restrict the breaker plunger from fully retracting.
- With the vacuum applied, turn the adjusting screw until the centering bubble of the angle gauge is level.
See Figure 7
- Connect a rubber band to the vacuum break lever of the intermediate choke shaft.
- Open the throttle to allow the choke valve to close.
- Set up the angle gauge and set the angle to specification.
- Using a vacuum source, retract the vacuum break plunger.
The air valve rod must not restrict the vacuum break plunger from fully retracting.
- With the vacuum applied, turn the adjusting screw or bend the vacuum break rod until the bubble of the angle gauge is centered.
See Figure 8
- Loosen the lock screw and turn the tension adjusting screw counterclockwise until the air valve partly opens.
- Turn the tension adjusting screw clockwise until the air valve just closes, then turn the screw clockwise a specified number of turns.
- Tighten the lock screw and apply lithium grease to the spring contact area.
See Figure 9
- Using a vacuum source, seat the vacuum break plunger. The air valve must be closed.
- Insert a 0.025 inch plug gauge between the rod and the end of the slot.
- To adjust, bend the air valve rod.
See Figure 10
- If the choke cover plate is riveted, drill out the rivets and remove the plate assembly.
- Place the fast idle cam follower on the high step of the fast idle cam.
- Lift up on the choke lever to close the choke valve and insert a 0.120 inch plug gauge into the choke housing hole. The choke lever should just touch the gauge.
- To adjust, bend the choke rod.
- To replace the cover plate, rivet in place.
See Figure 11
- Connect a rubber band to the green tang of the intermediate choke shaft.
- Open the throttle to allow the choke valve to close.
- Set up the angle gauge and set the angle to specifications.
- Place the cam follower on the second step of the fast idle cam, against the rise of the first step. If the cam follower does not contact the cam, turn the fast idle screw additional turns.
- To adjust, bend the tang of the fast idle cam until the gauge bubble is centered.
The final fast idle speed adjustment must be performed according to the emission control label.Unloader Adjustment
See Figure 12
- Connect a rubber band to the green tang of the intermediate shaft.
- Open the throttle to allow the choke valve to close.
- Set up the angle gauge and set the angle to specification.
- Hold the secondary lockout lever away from the pin.
- Hold the throttle lever in the wide-open position.
- To adjust, bend the tang of the fast idle lever until the bubble of the angle gauge is centered.
See Figure 13
- With the choke and the throttle valves closed, insert a 0.015 inch plug gauge between the lockout lever and the pin. To establish clearance, bend the pin.
- Push down on the fast idle cam and hold the choke valve wide open.
- Insert a 0.015 inch plug gauge sideways between the lockout lever and the pin. To adjust, file the end of the pin.
See Figures 14 and 15
Before checking the mixture control solenoid travel, it may be necessary to modify the float gauge J-9789-130 or equivalent (used to externally check the float level).
This should be done by filing or grinding the sufficient material off the gauge to allow for insertion down the vertical D-shaped hole in the air horn casting (located next to the idle air bleed valve cover).
Check that the gauge freely enters the D-shaped vent hole and does not bind. The gauge will also be used to determine the total mixture control solenoid travel.
With the engine off and the air cleaner removed, measure the control solenoid travel as follows:
- Insert a modified float gauge J-9789-130 or equivalent down the D-shaped vent hole. Press down on the gauge and release it.
- Observe that the gauge moves freely and does not bind. With the gauge released (solenoid in the up position), be sure to read it at eye level and record the mark on the gauge (in inches) that lines up with the top of the air horn casting (upper edge).
- Lightly press down on the gauge until bottomed (solenoid in the down position). Record (in inches) the mark on the gauge that lines up with the top of the air horn casting.
- Subtract the gauge up dimension from gauge dimension. Record the difference (in inches). This difference is total solenoid travel.
- If total solenoid travel is not within 3 / 32 - 5 / 32 inch (2.4-3.9mm), perform the mixture control solenoid adjustments. If the difference is within 3 / 32 - 5 / 32 inch (2.4-3.9mm), proceed to the idle air bleed valve adjustment.
If adjustment is required, it will be necessary to remove the air horn and drive out the mixture control solenoid screw plug from the under side of the air horn.Adjustments
Before making adjustment to mixture control solenoid, verify that the plunger travel is not correct.
- Remove air horn, mixture control solenoid plunger, air horn gasket and plastic filler block, using normal service procedures.
Check carburetor for cause of incorrect mixture:
- M/C solenoid bore or plunger worn or sticking
- Metering rods for incorrect part number, sticking or rods or springs not installed properly
- Foreign material in jets
- Remove throttle side metering rod. Install mixture control solenoid gauging tool, J-33815-1, BT-8253-A, or equivalent, over the throttle side metering jet rod guide and temporarily reinstall the solenoid plunger into the solenoid body.
- Holding the solenoid plunger in the DOWN position, use tool J-28696-10, BT-7928, or equivalent, to turn lean mixture solenoid screw counterclockwise until the plunger breaks contact with the gauging tool. Turn slowly clockwise until the plunger makes contact with the gauging tool. The adjustment is correct when the solenoid plunger is contacting both the solenoid stop and the gauging tool.
If the total difference in adjustment required less than3/4turn of the lean mixture solenoid screw, the original setting was within the manufacturer's specifications.
- Remove solenoid plunger and gauging tool and reinstall metering rod and plastic filler block.
- Invert air horn and remove rich mixture stop screw from bottom side of air horn, using tool J-28696-4, BT-7967-A, or equivalent.
- Remove lean mixture screw plug and the rich mixture stop screw plug from air horn, using a suitable sized punch.
- Reinstall rich mixture stop screw in air horn and bottom lightly, then back screw out 1 / 4 turn.
- Reinstall air horn gasket, mixture control solenoid plunger and air horn to carburetor.
Adjust M/C Solenoid Plunger travel as follows:
- Insert float gauge down D-shaped vent hole. Press down on gauge and release, observing that the gauge moves freely and does not bind. With gauge released, (plunger UP position), read at eye level and record the reading of the gauge mark (in inches) that lines up with the top of air horn casting, (upper edge).
- Lightly press down on gauge until bottomed, (plunger DOWN position). Read and record (in inches) the reading of the gauge mark that lines up with top of air horn casting.
- Subtract gauge UP position (Step 1) from gauge DOWN position (Step 2) and record the difference. This difference is the total plunger travel. Insert external float gauge in vent hole and, with tool J-28696-10, BT-7928, or equivalent, adjust rich mixture stop screw to obtain 5 / 32 inch (3.9mm) total plunger travel.
With solenoid plunger travel correctly set, install plugs (supplied in service kits) in the air horn, as follows:
- Install plug, hollow end down, into the access hole to lean mixture (solenoid) screw. Use suitably sized punch to drive plug into the air horn until the top of plug is even with the lower. Plug must be installed to retain the screw setting and to prevent fuel vapor loss.
- Install plug, with hollow end down, over the rich mixture stop screw access hole and drive plug into place so that the top of the plug is 3 / 16 inch (4.7mm) below the surface of the air horn casting. Plug must be installed to retain screw setting.
- To check the M/C solenoid dwell, first disconnect vacuum line to the canister purge valve and plug it. Ground diagnostic TEST terminal and run engine until it is at normal operation temperature (upper radiator hose hot) and in closed loop.
- Check M/C dwell at 3000 rpm. If within 10-50 degrees, calibration is complete. If higher than 50 degrees, check carburetor for cause of rich condition. If below 10 degrees, look for cause of lean engine condition such as vacuum leaks. If none found, check for cause of lean carburetor.
See Figures 16, 17 and 18
A cover is in place over the idle air bleed valve and the access holes to the idle mixture needles are sealed with hardened plugs, to seal the factory settings, during original equipment production. These items are NOT to be removed unless required for cleaning, part replacement, improper dwell readings or if the System Performance Check indicates the carburetor is the cause of the trouble.
- With engine OFF , cover the internal bowl vents and inlet to bleed valve and the carburetor air intakes with masking tape, to prevent metal chips from entering.
- Carefully drill rivet head of idle air bleed cover, with 0.110 in. drill bit.
- Remove rivet head and all pieces of rivet.
- Lift cover off air bleed valve and blow out any metal shavings, or use a magnet to remove excess metal.
- Remove masking tape.
- Start engine allow to reach normal operating temperature.
- Disconnect the vacuum hose from the canister purge valve and plug it.
- While idling in D for automatic transmission or N for manual transmission, slowly turn the valve counterclockwise or clockwise, until the dwell reading varies within the 25-35 degree range, attempting to be as close to 30 degrees as possible.
Perform this step carefully. The air bleed valve is very sensitive and should be turned in1/8turn increments only.
- If the dwell reading does not vary and is not within the 25-35 degree range, it will be necessary to remove the plugs and to adjust the idle mixture needles.
See Figures 19 and 20
- Using tool J-29030-B, BT-7610-B, or equivalent, turn each idle mixture needle clockwise until lightly seated, then turn each mixture needle counterclockwise 3 turns.
- Reinstall carburetor on engine, using a new flange mounting gasket, but do not install air cleaner or gasket at this time.
- Disconnect vacuum hose to canister purge valve and plug it.
- Start engine and allow it to reach normal operating temperature.
- While idling in D ( N for manual transmission), adjust both mixture needles equally, in 1 / 8 turn increments, until dwell reading varies within the 25-35 degree range, attempting to be as close to 30 degrees as possible.
- If reading is too low, turn mixture needles counterclockwise. If reading is too high, turn mixture needles clockwise. Allow time for dwell reading to stabilize after each adjustment.
After adjustments are complete, seal the idle mixture needle openings in the throttle body, using silicone sealant, RTV rubber, or equivalent. The sealer is required to discourage unnecessary readjustment of the setting and prevent fuel vapor loss in that area.
- On vehicles without a carburetor-mounted Idle Load Compensator, adjust curb idle speed if necessary.
- Check, and if necessary, adjust fast idle speed, as described on the Vehicle Emission Control Information label.
See Figure 21
The idle load compensator is adjusted at the factory. Do not make any adjustments unless diagnosis or curb idle speed is not to specification.
- Make certain ignition timing, mixture adjustment, vacuum hoses, fuel pressure and CCC system meets specifications.
- Remove air cleaner and plug hose to thermal vacuum valve.
- Connect a tachometer.
- Disconnect and plug hose to EGR valve.
- Disconnect and plug hose to canister purge port.
- Disconnect and plug hose to idle load compensator.
- Back out idle stop screw on carburetor 3 turns.
- Turn air conditioning OFF .
- Block drive wheels, set parking brake, place transmission in P , start and warm engine to normal operating temperature. Make certain choke is OPEN .
- With engine RUNNING place transmission in D and idle load compensator fully extended (no vacuum applied). Using tool J-29607, or equivalent, adjust plunger to obtain 650-750 rpm. Locknut on plunger must be held with a wrench to prevent damage to guide tabs.
- Measure distance from the locknut to tip of the plunger. This distance must not exceed 1 inch (25mm). If it does check for low idle condition.
- Reconnect vacuum hose to idle load compensator and observe idle speed.
- Idle speed should be 425-475 rpm in D .
- If idle speed is correct no further adjustment is necessary, proceed with Step 18. If idle speed is still incorrect continue with Step 15.
It may be necessary to remove the idle load compensator from the engine unless a hex key wrench is modified to clear obstructions.
- Stop engine, remove rubber cap from the center outlet tube.
- Using a 0.90 inch hex wrench, insert through open center tube to engage idle speed adjusting screw.
- If idle speed in Step 13, was low turn the adjusting screw counterclockwise 1 turn for every 85 rpm low. If idle speed was high turn screw 1 turn for every 85 rpm high.
- Disconnect and plug vacuum hose to the idle load compensator.
- Using a hand pump, apply vacuum to the idle load compensator until fully retracted.
- Adjust the idle stop screw on carburetor float bowl to obtain 450 rpm in D .
- Place transmission in P and stop engine.
- Reconnect the idle load compensator.
- Reconnect all vacuum hoses.
- Install air cleaner and gasket. Remove wheel blocks.
See Figures 22 and 23
Before the throttle position sensor voltage output setting can be accurately checked or adjusted the idle rpm must be within specifications. The plug covering the TPS adjustment screw is used to provide a tamper-resistant design and retain the factory setting during vehicle operation. Do not remove the plug unless diagnosis indicates the TPS is not adjusted correctly, or it is necessary to replace the air horn assembly, float bowl, TPS, or TPS adjustment screw. This is a critical adjustment that must be performed accurately to ensure proper vehicle performance and control of exhaust emissions. Remove TPS plug if not already removed.
Adjustment is required only if voltage is above the following readings, as the ECM automatically zeros below 0.70 Volts.
- Using a 5 / 64 inch (2 mm) drill bit, carefully drill a hole in the steel or aluminum plug. Be sure to drill only far enough to start a self tapping screw, the approximate drilling depth is 1 / 16 - 1 / 8 inch.
Use care in drilling so as not to damage the TPS adjustment screw head.
- Start a long self tapping screw (No. 8 x1 / 2 inch) into the drilled pilot hole in the plug. Turn the screw in only enough to ensure a good thread engagement in the drilled hole.
- Place a suitable tool between the screw head and the air horn casting. Then pry against the screw head to remove the plug. A small slide hammer may also be used in this procedure. Be sure to discard the plug when it has been removed.
- Connect a suitable digital voltmeter (J-29125 or equivalent) from the TPS connector center terminal (B) to the bottom terminal (C).
Jumper wires for access can be made using terminals 12014836 and 12014837 or equivalent. Make jumper wires up with 16 gauge (1.0mm), 18 gauge (0.8mm) or 20 gauge (0.5mm) wire approximately 6 in. long.
- With the ignition ON and the engine stopped, install the TPS adjustment screw and turn the screw with a suitable tool to obtain the specified voltage at the specified throttle position with the A/C controls in the OFF position.
- After the adjustment has been made, install a new plug kit (supplied in the service kits), into the air horn. Drive the plug into place until it is flush with the raised pump lever boss on the casting. Clear trouble code memory after adjustment.
The plug must be installed to retain the TPS adjustment screw setting. If a plug kit is not available, remove the TPS adjusting screw and apply thread sealer adhesive X-10 or equivalent to the screw threads. Now repeat the TPS adjustment procedure to obtain the correct TPS voltage.
REMOVAL & INSTALLATION
See Figure 24
Always replace all internal gaskets that are removed. Base gasket should be inspected and replaced only if damaged. Flooding, stumble on acceleration and other performance complaints are in many instances, caused by presence of dirt, water, or other foreign matter in carburetor. To aid in diagnosis, carburetor should be carefully removed from engine without draining fuel from bowl. Contents of fuel bowl may then be examined for contamination as carburetor is disassembled. Check fuel filter.
- Disconnect the battery and remove the air cleaner.
- Disconnect the accelerator linkage.
- Disconnect the transmission detent cable.
- If equipped, remove the cruise control.
- Disconnect all of the necessary vacuum lines.
- Disconnect the fuel line at the carburetor inlet. Place a rag beneath the line to soak up any fuel that spills, then dispose of the rag properly.
- Remove the attaching bolts and remove the carburetor.
- To install, position the carburetor onto the manifold and install the attaching bolts.
- Connect the fuel line at the carburetor inlet.
- Connect all of the vacuum lines.
- If equipped, install the cruise control cable.
- Connect the transmission detent cable.
- Connect the accelerator linkage.
- Install the air cleaner and connect the battery.
See Figure 25
Efficient carburetion depends greatly on careful cleaning and inspection during overhaul, since dirt, gum, water, or varnish in or on the carburetor parts are often responsible for poor performance.
Overhaul your carburetor in a clean, dust-free area. Carefully disassemble the carburetor, referring often to the exploded views and directions packaged with the rebuilding kit. Keep all similar and look-alike parts separated during disassembly and cleaning to avoid accidental interchange during assembly. Make a note of all jet sizes.
When the carburetor is disassembled, wash all parts (except diaphragms, electric components, pump plunger, and any other plastic, leather, fiber, or rubber parts) in clean carburetor solvent. Do not leave parts in the solvent any longer than is necessary to sufficiently loosen the deposits. Excessive cleaning may remove the special finish from the float bowl and choke valve bodies, leaving these parts unfit for service. Rinse all parts in clean solvent and blow them dry with compressed air or allow them to air dry. Wipe clean all cork, plastic, leather, and fiber parts with a clean, lint-free cloth.
Blow out all passages and jets with compressed air and be sure that there are no restrictions or blockages. Never use wire or similar tools to clean jets, fuel passages, or air bleeds. Clean all jets and valves separately to avoid accidental interchange.
Check all parts for wear or damage. If wear or damage is found, replace the defective parts. Especially check the following:
- Check the float needle and seat for wear. If wear is found, replace the complete assembly.
- Check the float hinge pin for wear and the float(s) for dents or distortion. Replace the float if fuel has leaked into it.
- Check the throttle and choke shaft bores for wear or an out-of-round condition. Damage or wear to the throttle arm, shaft, or shaft bore will often require replacement of the throttle body. These parts require a close tolerance of fit; wear may allow air leakage, which could affect starting and idling.
Throttle shafts and bushings are not included in overhaul kits. They can be purchased separately or repaired by a qualified carburetor overhaul shop.
- Inspect the idle mixture adjusting needles for burrs or grooves. Any such condition requires replacement of the needle, since you will not be able to obtain a satisfactory idle.
- Test the accelerator pump check valves. They should pass air one way but not the other. Test for proper seating by blowing and sucking on the valve. Replace the valve check ball and spring as necessary. If the valve is satisfactory, wash the valve parts again to remove breath moisture.
- Check the bowl cover for warped surfaces with a straightedge.
- Closely inspect the accelerator pump plunger for wear and damage, replacing as necessary.
- After the carburetor is assembled, check the choke valve for freedom of operation.
Carburetor overhaul kits are recommended for each overhaul. These kits contain all gaskets and new parts to replace those which deteriorate most rapidly. Failure to replace all parts supplied with the kit (especially gaskets) can result in poor performance later.
Some carburetor manufacturers supply overhaul kits for three basic types: minor repair; major repair; and gasket kits. Basically, they contain the following:Minor Repair Kits:
After cleaning and checking all components, reassemble the carburetor, using new parts and referring to the exploded view. When reassembling, make sure that all screws and jets are tight in their seats, but do not overtighten as the tips will be distorted. Tighten all screws gradually, in rotation. Do not tighten needle valves into their seats; uneven jetting will result. Always use new gaskets. Be sure to follow all assembly and adjustment procedures.
Before performing any service on the carburetor, it is essential that it be placed on a suitable holding fixture, such as tool J-9789-118, BY-30-15 or equivalent. Without the use of the holding fixture, it is possible to damage throttle valves or other parts of the carburetor.Carburetor Disassembly
IDLE SPEED CONTROL (ISC) SOLENOID REMOVAL
Remove the attaching screws, then remove the Idle Speed Control solenoid (ISC). The ISC should not be immersed in any carburetor cleaner. They must always be removed before complete carburetor overhaul, as carburetor cleaner will damage the internal components.IDLE MIXTURE NEEDLE PLUG REMOVAL
- Use a hacksaw to make 2 parallel cuts in the throttle body, 1 on each side of the locator points near an idle mixture needle plug. The distance between the cuts will depend on the size of the punch to be used. Cuts should reach down to the steel plug, but should but extend more than 1 / 8 inch beyond the locator points.
- Place a flat punch at a point near the ends of the saw marks in the throttle body. Hold the punch at a 45 degree angle and drive it into the throttle body until the casting breaks away, exposing the hardened steel plug. The plug will break, rather than remaining intact. Remove all the loose pieces.
- Repeat the procedure for the other idle mixture needle plug.
- Cover internal bowl vents and air inlets to the bleed valve with masking tape.
- Carefully align a 7 / 64 inch drill bit on rivet head. Drill only enough to remove head of each rivet holding the idle air bleed valve cover.
- Use a suitably sized punch to drive out the remainder of the rivet from the castings. Repeat procedure with other rivet.
- Lift off cover and remove any pieces of rivet still inside tower. Use shop air to blow out any remaining chips.
- Remove idle air bleed valve from the air horn.
- Remove and discard O-ring seals from valve. New O-ring seals are required for reassembly. The idle air bleed valve is serviced as a complete assembly only.
See Figures 26 and 27
- Remove upper choke lever from the end of choke shaft by removing retaining screw. Rotate upper choke lever to remove choke rod from slot in lever.
- Remove choke rod from lower lever inside the float bowl casting. Remove rod by holding lower lever outward with small suitable tool and twisting rod counterclockwise.
- Remove secondary metering rods by removing the small screw in the top of the metering rod hanger. Lift upward on the metering rod hanger until the secondary metering rods are completely out of the air horn. Metering rods may be disassembled from the hanger by rotating the ends out of the holes in the end of the hanger.
- Remove pump link retainer and remove link from pump lever.
Do not attempt to remove the lever, as damage to the air horn could result.
- Remove the front vacuum break hose from tube on float bowl.
- Remove 11 air horn-to-bowl screws; then remove the 2 countersunk attaching screws located next to the venturi. If used, remove secondary air baffle deflector from beneath the 2 center air horn screws.
- Remove air horn from float bowl by lifting it straight up. The air horn gasket should remain on the float bowl for removal later.
When removing air horn from float bowl, use care to prevent damaging the mixture control solenoid connector, Throttle Position Sensor (TPS) adjustment lever and the small tubes protruding from the air horn. These tubes are permanently pressed into the air horn casting. Do not remove them. Do not place vacuum break assembly in carburetor cleaner, as damage to vacuum break will occur.
- Remove front vacuum break bracket attaching screws. The vacuum break assembly may now be removed from the air valve dashpot rod and the dashpot rod from the air valve lever.
- Remove TPS plunger by pushing plunger down through seal in air horn.
- Remove TPS seal and pump plunger stem seal by inverting air horn and using a small suitable tool to remove staking holding seal retainers in place. Remove and discard retainers and seals.
Use care in removing the TPS plunger seal retainer and pump plunger stem seal retainer to prevent damage to air horn casting. New seals and retainers are required for reassembly.
- Invert air horn and use tool J-28696-4, BT-7967A, or equivalent, to remove rich mixture stop screw and spring.
- Use a suitable punch to drive the lean mixture screw plug and rich mixture stop screw plug out of the air horn. Discard the plugs.
- Further disassembly of the air horn is not required for cleaning purposes.
The choke valve and choke valve screws, the air valves and air valve shaft should not be removed. However, if it is necessary to replace the air valve closing springs or center plastic eccentric cam, a repair kit is available. Instructions for assembly are included in the repair kit.FLOAT BOWL DISASSEMBLY
See Figures 28 and 29
- Remove solenoid metering rod plunger by lifting straight up.
- Remove air horn gasket by lifting it from the dowel locating pins on float bowl. Discard gasket.
- Remove pump plunger from pump well.
Remove staking holding Throttle Position Sensor (TPS) in bowl as follows:
- Lay a flat tool or metal piece across bowl casting to protect gasket sealing surface.
- Use a small suitable tool to depress TPS sensor lightly and hold against spring tension.
- Observing safety precautions, pry upward with a small prybar, or other suitable tool, to remove bowl staking, making sure prying force is exerted against the metal piece and not against the bowl casting. Use care not to damage the TPS sensor.
- Push up from bottom on electrical connector and remove TPS and connector assembly from bowl. Use care in removing sensor and connector assembly to prevent damage to this critical electrical part.
- Remove spring from bottom of TPS well in float bowl.
- Remove plastic bowl insert from float bowl.
- Carefully lift each metering rod out of the guided metering jet, checking to be sure the return spring is removed with each metering rod.
Use extreme care when handling these critical parts to avoid damage to the metering rod and spring.
Remove the mixture control solenoid from the float bowl as follows:
- Remove screw attaching solenoid connector to float bowl. Do not remove solenoid connector from float bowl until called for in text.
- Use tool J-28696-10, BT-7928, or equivalent, to remove lean mixture (solenoid) screw. Do not remove plunger return spring or connector and wires from the solenoid body. The mixture control solenoid, with plunger and connector, is only serviced as a complete assembly.
- Remove rubber gasket from top of solenoid connector and discard.
- Remove solenoid screw tension spring (next to float hanger pin).
- Remove float assembly and float needle by pulling up on retaining pin. Remove needle and seat and gasket using set remover tool J-22769, BT-3006M, or equivalent.
- Remove large mixture control solenoid tension spring from boss on bottom of float bowl located between guided metering jets.
- If necessary, remove the primary main metering jets using special tool J-28696-4, BT-7928, or equivalent.
Use care installing tool on jet, to prevent damage to the metering rod guide (upper area), and locating tool over vertical float sections on lower area of jet. Also, no attempt should be made to remove the secondary metering jets (metering orifice plates). These jets are fixed and, if damaged, entire bowl replacement is required.
- Remove pump discharge check ball retainer and turn bowl upside down, catching discharge ball as it falls.
- Remove secondary air baffle, if replacement is required.
- Remove pump well fill slot baffle only if necessary.
The tamper-resistant choke cover is used to discourage unnecessary readjustment of the choke thermostatic cover and coil assembly. However, if it is necessary to remove the cover and coil assembly during normal carburetor disassembly for cleaning and normal carburetor disassembly for cleaning and overhaul, the procedures below should be followed.
- Support float bowl and throttle body, as an assembly, on a suitable holding fixture such as tool J-9789-118, BT-30-15, or equivalent.
- Carefully align a 5 / 32 inch drill (0.159 inch) on rivet head and drill only enough to remove rivet head. Drill the 2 remaining rivet heads, then use a drift and small hammer to drive the remainder of the rivets out of the choke housing.
Use care in drilling to prevent damage to the choke cover or housing.
- Remove the 2 conventional retainers, retainer with tab and choke cover assembly from choke housing.
- Remove choke housing assembly from float bowl by removing retaining screw and washer inside the choke housing. The complete choke assembly can be removed from the float bowl by sliding outward.
- Remove secondary throttle valve lock-out lever from float bowl.
- Remove lower choke lever from inside float bowl cavity by inverting bowl.
- To disassemble intermediate choke shaft from choke housing, remove coil lever retaining screw at end of shaft inside the choke housing. Remove thermostatic coil lever from flats on intermediate choke shaft.
- Remove intermediate choke shaft from the choke housing by sliding it outward. The fast idle cam can now be removed from the intermediate choke shaft. Remove the cup seal from the float bowl cleaning purposes. Do not attempt to remove the insert.
- Remove fuel inlet nut, gasket, check valve, filter assembly and spring. Discard check valve filter assembly and gasket.
- Remove 3 throttle body-to-bowl attaching screws and lockwashers and remove throttle body assembly.
- Remove throttle body-to-bowl insulator gasket.
Place throttle body assembly on carburetor holding fixture to avoid damage to throttle valves.
- Remove pump rod from the throttle lever by rotating the rod until the tang on the rod aligns with the slot in the lever.
- Use tool J-29030-B, BT-7610B, or equivalent, to remove idle mixture needles for thorough throttle body cleaning.
- Further disassembly of the throttle body is not required for cleaning purposes. The throttle valve screws are permanently staked in place and should not be removed. The throttle body is serviced as a complete assembly.
The carburetor parts should be cleaned in a cold immersion-type cleaner such as Carbon X (X-55) or equivalent.
The idle speed solenoid, the mixture control solenoid, the throttle position sensor, the electric choke, the rubber parts, the plastic parts, the diaphragms, the pump plunger, the plastic filler block, should not be immersed in carburetor cleaner as they will hardened, swell or distort.The plastic busing in the throttle lever will withstand normal cleaning in the carburetor cleaner. Thoroughly clean all of the metal parts and blow dry with shop air. Make sure all the fuel passages and metering parts are free of burrs and dirt. Do not pass the drills or wires through the jets and passages.
- Inspect the upper and lower surface of the carburetor castings for damage.
- Inspect the holes in the levers for excessive wear or out of round conditions. If worn, the levers should be replaced. Inspect the plastic bushings in the levers for damage and excessive wear, replace as required.
- Check, repair or replace parts, if the following problems are encountered:
- Inspect the float valve and seat for dirt, deep wear grooves, scores and improper sealing.
- Inspect the float valve pull clip for proper installation; be careful not to bend the pull clip.
- Inspect the float, the float arms and the hinge pin for distortion, binds, and burrs. Check the density of the material in the float; if heavier than normal, replace the float.
- Clean or replace the fuel inlet filter and check the valve assembly.
- Inspect the pump plunger for cracks, scores or cup excessive wear. A used pump cup will shrink when dry. If dried out, soak in fuel for 8 hours before testing.
- Inspect the pump duration and return springs for weakness or distortion.
- Check the pump passages and the jet(s) for dirt, improper seating of the discharge checkball or the temperature bypass disc and/or scores in the pumpwell. Check the condition of the pump discharge check ball spring, replace as necessary.
- Check the pump linkage for excessive wear; repair or replace as necessary.
- Check the choke valve and linkage for excessive wear, binds or distortion.
- Test the vacuum break diaphragm(s) for leaks.
- Clean or replace the fuel filter.
- Inspect the float valve for sticking, dirt, etc.
- Also check the items under "Flooding".
- Clean all fuel and vacuum passages in the castings.
- Check the choke valve for freedom of movement.
- Check the Mixture Control solenoid for sticking or binding.
- Inspect the metering jet for dirt, loose parts or damage.
Do not attempt to readjust the mixture screw located inside the metering jet. The screw if factory adjusted and a change can upset the fuel system calibration. No attempt should be made to change this adjustment in the field except as the result of a Computer Command Control system performance check.
- Check the air valve and secondary metering rod for binding conditions. If the air valve or metering rod is damaged or the metering rod adjustment is changed from the factory setting, the air horn assembly must be replaced. Also check the air valve lever spring for proper installation (tension against the air valve shaft pin.
- Inspect the gasket and gasket mating surfaces on the casting for nicks, burrs or damage to the sealing beads.
- Check the operation and sealing of the mixture control solenoid.
- Clean all of the idle field passages.
- If removed, inspect the idle mixture needle for ridges, burrs or being bent.
- Check the throttle lever and valves for binds, nicks. or other damage.
- Check all of the diaphragms for possible ruptures or leaks.
See Figures 30, 31 and 32
- Install the lower end of the pump rod in the throttle lever by aligning the tang on the rod with the slot in the lever. The end of the rod should point outward toward the throttle lever.
- Install idle mixture needles and springs using tool J-29030-B, BT-07610B, or equivalent. Lightly seat each needle and then turn counterclockwise the number of specified turns, the final idle mixture adjustment is made on the vehicle.
- If a new float bowl assembly is used, stamp or engrave the model number on the new float bowl. Install new throttle body-to-bowl insulator gasket over 2 locating dowels on bowl.
- Install throttle body making certain throttle body is properly located over dowels on float bowl. Install 3 throttle body-to-bowl screws and lockwashers and tighten evenly and securely.
- Place carburetor on proper holding fixture such as J-9789-118, BT-30-15 or equivalent.
- Install fuel inlet filter spring, a new check valve filter assembly, new gasket and inlet nut. Tighten nut to 18 ft. lbs. (24 Nm).
When installing a service replacement filter, make sure the filter is the type that includes the check valve to meet government safety standard. New service replacement filters with check valve meet this requirement. When properly installed, the hole in the filter faces toward the inlet nut. Ribs on the closed end of the filter element prevent it from being installed incorrectly, unless forced. Tightening beyond the specified torque can damage the nylon gasket.
- Install a new cup seal into the insert on the side of the float bowl for the intermediate choke shaft. The lip on the cup seal faces outward.
- Install the secondary throttle valve lock-out lever on the boss of the float bowl, with the recess hole in the lever facing inward.
- Install the fast idle cam on the intermediate choke shaft (steps on cam face downward).
- Carefully install fast idle cam and intermediate choke shaft assembly in the choke housing. Install the thermostatic coil lever on the flats on the intermediate choke shaft. Inside thermostatic choke coil lever is properly aligned when both inside and outside levers face toward the fuel inlet. Install inside lever retaining screw into the end of the intermediate choke shaft.
- Install lower choke rod (inner) lever into cavity in float bowl.
- Install choke housing to bowl, sliding intermediate choke shaft into lower (inner) lever. tool J-23417, BT-6911 or equivalent, can be used to hold the lower choke lever in correct position while installing the choke housing. The intermediate choke shaft lever and fast idle cam are in correct position when the tang on lever is beneath the fast idle cam.
- Install choke housing retaining screws and washers. Check linkage for freedom of movement. Do not install choke cover and coil assembly until inside coil lever is adjusted.
- If removed, install air baffle in secondary side of float bowl with notches toward the top. Top edge of baffle must be flush with bowl casting.
- If removed, install baffle inside of the pump well with slot toward the bottom.
- Install pump discharge check ball and retainer screw in the passage next to the pump well.
- If removed, carefully install primary main metering jets in bottom of float bowl using tool J-28696-4, BT-7928, or equivalent.
Use care in installing jets to prevent damage to metering rod guide.
- Install large mixture control solenoid tension spring over boss on bottom of float bowl.
- Install needle seat assembly, with gasket, using seat installer J-22769, BT-3006M, or equivalent.
- To make adjustment easier, carefully bend float arm before assembly.
- Install float needle onto float arm by sliding float lever under needle pull clip. Proper installation of the needle pull clip is to hook the clip over the edge of the float on the float arm facing the float pontoon.
- Install float hinge pin into float arm with end of loop of pin facing pump well. Install float assembly by aligning needle in the seat and float hinge pin into locating channels in float bowl. Do not install float needle pull clip into holes in float arm.
- Perform a float level adjustment, as necessary.
- Install mixture control solenoid screw tension spring between raised bosses next to float hanger pin.
Install mixture control solenoid and connector assembly as follows:
- Install new rubber gasket on top of solenoid connector.
- Install solenoid carefully in the float chamber, aligning pin on end of solenoid with hole in raised boss at bottom of bowl. Align solenoid connector wires to fit in slot in bowl.
- Install lean mixture (solenoid) screw through hole in solenoid bracket and tension spring in bowl, engaging first 6 screw threads to assure proper thread engagement.
- Install mixture control solenoid gauging tool J-33815-1, BT-8253-A, or equivalent over the throttle side metering jet rod guide and temporarily install solenoid plunger.
- Holding the solenoid plunger against the solenoid stop, use tool J-28696-10, BT-7928, or equivalent, to turn the lean mixture (solenoid) screw slowly clockwise, until the solenoid plunger just contacts the gauging tool. The adjustment is correct when the solenoid plunger is contacting both the solenoid stop and the gauging tool.
- Remove solenoid plunger and gauging tool.
- Install connector attaching screw, but do not overtighten, as that could cause damage to the connector.
- Install Throttle Position Sensor (TPS) return spring in bottom of well in float bowl.
- Install the TPS and connector assembly in float bowl by aligning groove in electrical connector with slot in float bowl casting. Push down on connector and sensor assembly so that connector and wires are located below bowl casting surface.
- Install plastic bowl insert over float valve, pressing downward until properly seated (flush with bowl casting surface).
- Slide metering rod return spring over metering rod tip until small end of spring stops against shoulder on rod. Carefully install metering rod and spring assembly through holding in plastic bowl insert and gently lower the metering rod into the guided metering jet, until large end of spring seats on the recess on end of jet guide.
Do not force metering rod down in jet. Use extreme care when handling these critical parts to avoid damage to rod and spring. If service replacement metering rods, springs and jets are installed, they must be installed in matched sets.
- Install pump return spring in pump well.
- Install pump plunger assembly in pump well.
- Holding down on pump plunger assembly against return spring tension, install air horn gasket by aligning pump plunger stem with hole in gasket and aligning holes in gasket over TPS plunger, solenoid plunger return spring metering rods, solenoid attaching screw and electrical connector. Position gasket over the 2 dowel locating pins on the float bowl.
- Holding down on air horn gasket and pump plunger assembly, install the solenoid-metering rod plunger in the solenoid, aligning slot in end of plunger with solenoid attaching screw. Be sure plunger arms engage top of each metering.
- If a service replacement mixture control solenoid package is installed, the solenoid and plunger MUST be installed as a matched set.
- If removed, install Throttle Position Sensor (TPS) adjustment screw in air horn using tool J-28696-10, BT-7967A, or equivalent. Final adjustment of the TPS is made on the vehicle.
- Inspect the air valve shaft pin for lubrication. Apply a liberal quantity of lithium base grease to the air valve shaft pin, especially in the area contacted by the air valve spring.
- Install new pump plunger and TPS plunger seals and retainers in air horn casting. The lip on the seal faces outward, away from the air horn mounting surface. Lightly stake seal retainer in 3 places, choosing locations different from the original stakings.
- Install rich mixture stop screw and rich authority adjusting spring from bottom side of the air horn. Use tool J-2869-4, BT-7967A, or equivalent, to bottom the stop screw lightly, then back out 1 / 4 turn. Final adjustment procedure will be covered later in this section.
- Install TPS actuator plunger in the seal.
- Carefully lower the air horn assembly onto the float bowl while positioning the TPS adjustment lever over the TPS sensor and guiding pump plunger stem through the seal in the air horn casting. To ease installation, insert a thin suitable tool between the air horn gasket and float bowl to raise the TPS Adjustment Lever, positioning it over the TPS sensor.
- Make sure that the bleed tubes and accelerating well tubes are positioned properly through the holes in the air horn gasket. Do not force the air horn assembly onto the bowl, but lower it lightly into place over the 2 dowel locating pins.
- Install 2 long air horn screws and lockwashers, 9 short screws and lockwashers and 2 countersunk screws located next to the carburetor venturi area. Install secondary air baffle beneath the No. 3 and 4 screws. Tighten all screws evenly and securely.
- Install air valve rod into slot in the lever on the end of the air valve shaft. Install the other end of the rod in hole in front vacuum break plunger. Install front vacuum break and bracket assembly on the air horn, using 2 attaching screws. Tighten screw securely. Connect pump link to pump lever and install retainer.
Use care installing the roll pin to prevent damage to the pump lever bearing surface and casting bosses.
- Install 2 secondary metering rods into the secondary metering rod hanger (upper end of rods point toward each other). Install secondary metering rod holder, with rods, onto air valve cam follower. Install retaining screw and tighten securely. Work air valves up and down several times to make sure they remove freely in both directions.
- Connect choke rod into lower choke lever inside bowl cavity. Install choke rod in slot in upper choke lever. Position the lever on end of choke shaft, making sure flats on end of shaft align with flats in lever. Install attaching screw and tighten securely. When properly installed, the number on the lever will face outward.
Adjust the rich mixture stop screw:
- Insert external float gauging tool J-34935-1, BT-8420A, or equivalent, in the vertical D-shaped vent hole in the air horn casting (next to the idle air bleed valve) and allow it to float freely.
- Read (at eye level) the mark on the gauge, in inches, that lines up with the tip of the air horn casting.
- Lightly press down on gauge, reading and recording the mark on the gauge that lines up with the top of the air horn casting.
- Subtract gauge UP dimension, found in Step b, from gauge DOWN dimension, found in Step c and record the difference in inches. This difference in dimension is the total solenoid plunger travel.
- Insert tool J-28696-10, BT-7928, or equivalent, in the access hole in the air horn and adjust the rich mixture stop screw to obtain 1 / 8 inch total solenoid plunger travel.
With the solenoid plunger travel correctly set, install the plugs supplied in the service kit into the air horn to retain the setting and prevent fuel vapor loss:
- Install the plug, hollow end down, into the access hole to the lean mixture (solenoid) screw and use a suitably sized punch to drive the plug into the air horn until top of plug is even with the lower edge of the hole chamber.
- In a similar manner, install the plug over the rich mixture screw access hole and drive the plug into place so that the tip of the plug is 1 / 16 inch below the surface of the air horn casting.
Install the idle air bleed valve as follows:
- Lightly coat 2 new O-ring seals with automatic transmission fluid, to aid in their installation on the idle air bleed valve body. The thick seal goes in the upper groove and the thin seal goes in the lower groove.
- Install the idle air bleed valve in the air horn, making sure that there is proper thread engagement.
- Insert idle air bleed valve gauging tool J-33815-2, BT-8353B, or equivalent, in throttle side D-shaped vent hole of the air horn casting. The upper end of the tool should be positioned over the open cavity next to the idle air bleed valve.
- Hold the gauging tool down lightly so that the solenoid plunger is against the solenoid stop, then adjust the idle air bleed valve so that the gauging tool will pivot over and just contact the top of the valve.
- Remove the gauging tool.
- The final adjustment of the idle air bleed valve is made on the vehicle to obtain idle mixture control.
- Perform the air valve spring adjustment and choke coil Lever Adjustment.
Install the cover and coil assembly in the choke housing, as follows:
- Place the cam follower on the highest step of the fast idle cam.
- Install the thermostatic cover and coil assembly in the choke housing, making sure the coil tang engages the inside coil pickup lever. Ground contact for the electric choke is provided by a metal plate located at the rear of the choke cover assembly. Do not install a choke cover gasket between the electric choke assembly and the choke housing.
- A choke cover retainer kit is required to attach the choke cover to the choke housing. Follow the instructions found in the kit and install the proper retainer and rivets using a suitable blind rivet tool.
- It may be necessary to use an adapter (tube) if the installing tool interferes with the electrical connector tower on the choke cover.
- Install the hose on the front vacuum brake and on the tube on the float bowl.
- Position the idle speed solenoid and bracket assembly on the float bowl, retaining it with 2 large countersunk screws.
- Perform the choke rod-fast idle cam adjustment, primary (front) vacuum break adjustment, air valve rod adjustment-front, unloader adjustment and the secondary lockout adjustment.
- Reinstall the carburetor on the vehicle with a new flange gasket.