See Figures 1, 2, 3 and 4
Efficient carburetion depends greatly on careful cleaning and inspection during overhaul, since dirt, gum, water or varnish in or on the carburetor parts are often responsible for poor performance.
Overhaul your carburetor in a clean, dust-free area. Carefully disassemble the carburetor, referring often to the exploded views and directions packaged with the rebuilding kit. Keep all similar and look-alike parts segregated during disassembly and cleaning to avoid accidental interchange during assembly. Make a note of all jet sizes.
When the carburetor is disassembled, wash all parts (except diaphragms, electric choke units, solenoids, pump plunger and any other plastic, leather, fiber or rubber parts) in clean carburetor solvent. DO NOT leave the 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 the 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 fitting tolerance; 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.
- 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 of three basic types: minor repair, major repair and gasket kits. Basically, they contain the following:Minor Repair Kits:
Major Repair Kits:
After cleaning and checking all components, reassembly 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, for the tips will be distorted. Tighten all screws gradually, in rotation. DO NOT tighten the needle valves into their seats; uneven jetting will result. Always use new gaskets. Be sure to adjust the float level when reassembling.
Idle Speed Solenoid Removal
Remove the attaching screws, then remove the Idle Speed Solenoid. The Idle Speed Solenoid should not be immersed in any carburetor cleaner, and should always be removed before complete carburetor overhaul, as carburetor cleaner will damage the internal components.Idle Mixture Needle Plug Removal
- Use hacksaw to make two parallel cuts in the throttle body, one on each side of the locator points near one 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 in. (3mm) 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° 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 in. 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.
- 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 screwdriver 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 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.
- 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.
Do not place vacuum break assembly in carburetor cleaner, as damage to vacuum break will occur.
- Remove Throttle Position Sensor (TPS) plunger by pushing plunger down through seal in air horn.
- Remove the throttle position solenoid seal and pump plunger stem seal by inverting air horn and using a small screwdriver to remove staking holding seal retainers in place. Remove and discard retainers and seals.
Use care in removing the throttle position solenoid 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
The following special tools, or their equivalents, will be necessary for this procedure: J-28696-10, BT-7928, J-22769, BT-3006M, J-28696-4, and BT-7928.
- 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 screwdriver to depress throttle position solenoid sensor lightly and hold against spring tension.
- Observing safety precautions, pry upward with a small chisel or equivalent 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 throttle position solenoid sensor.
- Push up from bottom on electrical connector and remove throttle position solenoid 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 throttle position solenoid 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 if falls.
- Remove secondary air baffle, if replaced is required.
- Remove pump well fill slot baffle only if necessary.
Special tools J-9789-118, BT-30-15, or their equivalents, will be necessary for this procedure.
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 in. drill bit on the rivet head and drill only enough to remove the 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 for 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.
Special tools J-29030-B and BT-7610B, or their equivalents, will be necessary for this procedure.
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 following special tools, or their equivalents, will be necessary for this procedure: J-29030-B, BT-7610B, J-9789-118, BT-30-15, J-23417, BT-6911, J-28696-4, J-22769, BT-3006M, J-33815-1, BT-8253-A, J-28696-10, and BT-7928.
- 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-7610B, or equivalent. Lightly seat each needle and then turn counterclockwise 3 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, 18 ft. lbs (24 Nm), 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 or Tool J-28696-4, BT-7928, 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.
- Make 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 return spring in bottom of well in float bowl.
- Install throttle position sensor 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.
- 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 throttle position solenoid plunger, solenoid plunger return spring metering rods, solenoid attaching screw and electrical connector. Position gasket over the two 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 rod plunger.
- If a service replacement mixture control solenoid package is installed, the solenoid and plunger MUST be installed as a matched set.
The following special tools, or their equivalents, will be necessary for this procedure: J-28696-10, J-2869-4, BT-7967A, J-34935-1, BT-8420A, BT-7928, J-33815-2, and BT-8353B.
- If removed, install the throttle position solenoid adjustment screw in the air horn using Tool J-28696-10, BT-7967A, or equivalent. Final adjustment of the throttle position sensor 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 throttle position solenoid 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 three 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 throttle position solenoid actuator plunger in the seal.
- Carefully lower the air horn assembly onto the float bowl while positioning the throttle position solenoid adjustment lever over the throttle position solenoid sensor and guiding pump plunger stem through the seal in the air horn casting. To ease installation, insert a thin screwdriver between the air horn gasket and float bowl to raise the throttle position solenoid adjustment lever, positioning it over the throttle position solenoid 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 screws 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, and position 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, and again read and record 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 fractions of an inch. 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 in. (3mm) 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 in. (1.5mm) 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 as previously described.
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 as previously described.
- Reinstall the carburetor on the vehicle with a new flange gasket.