Carburetor - Rochester e4mc/e4me Pontiac Firebird III

COMPONENT TESTING

Note. Specific component testing information not available. Refer to any tests performed during REMOVAL & INSTALLATION or OVERHAUL procedures

APPLICATION

GENERAL MOTORS (ROCHESTER) CARBURETOR NO.

IDENTIFICATION

The Rochester E4MC and E4ME carburetor numbers are stamped vertically on the float bowl, near secondary throttle. If float bowl is replaced, follow manufacturer's instructions contained in service package to transfer part number to new float bowl. Some models have machined pump wells to reduce the pump well taper.

The E4MC and E4ME Quadrajet carburetors are used with the Computer Command Control (CCC) system. The first letter "E" indicates the carburetor is a part of the CCC system. The final letter, if "E", indicates the carburetor is equipped with an electric choke; if "C", a hot air choke.

Carburetor Identification Label. Scheme 1

DESCRIPTION

The E4MC and E4ME carburetors are of a 2-stage, downdraft design. The secondary circuit is composed of 2 large throttle bores, using the air valve principle, in which fuel is metered in direct proportion to the amount of air passing through the secondary throttle bores. A baffle is attached to the secondary side of the air horn, above the main well bleed tubes. This deflects incoming air to improve secondary nozzle operation on heavy acceleration.

The E4MC carburetor uses an air heated choke assembly; the E4ME, an electrically-actuated choke assembly. All E4MC and most E4ME models have 2 vacuum break diaphragm assemblies, primary and secondary, while some E4ME models have only primary vacuum break assembly.

Both the E4MC and E4ME models are used in conjunction with the Computer Command Control (CCC) system on General Motors vehicles. All carburetors are equipped with an electrically-actuated mixture control solenoid mounted in the float bowl. For all applications, fuel metering is controlled by stepped metering rods that operate in removable jets.

All models include tamper-resistant factory settings of the mixture control solenoid rich limit stop and lean mixture screw, idle air bleed valve, TPS, ILC, ISS and idle mixture screws. DO NOT adjust these except during major overhaul or replacement of air horn, float bowl or throttle body. Both electric and hot air chokes have riveted covers which must not be removed except for major overhaul.

Some General Motors engines equipped with A/C use an Idle Load Compensator (ILC) attached to the fuel bowl. The ILC adjusts curb idle speed by sensing changes in manifold vacuum (engine load). To prevent the ILC from reacting too quickly to vacuum changes, a differential Vacuum Delay Valve (DVDV) is installed between the ILC and vacuum source. The DVDV delays operation of the ILC until vacuum change is constant.

All other General Motors engines are equipped with an ISS on the fuel bowl. Controlled by the ECM, the ISS controls the normal curb idle speed and acts as a dashpot on deceleration at speeds above 40 MPH. When equipped with A/C, the ISS maintains a specific idle speed during A/C compressor operation.

THROTTLE POSITION SENSOR

The Throttle Position Sensor (TPS) is a variable resistor that is used to reflect changes in throttle valve angle. One terminal of the TPS is connected to a 5-volt source from the ECM, and another to ground. The third wire is connected to the ECM to measure voltage changes from the TPS.

IDLE STOP SOLENOID (ISS)

The solenoid is actuated by an ECM controlled relay for 2 operational modes

1. On A/C equipped vehicles, the idle stop solenoid is used to increase idle speed to compensate for A/C compressor load. When the climate control switch is moved to a position that turns on the A/C compressor, the ISS is energized and the plunger extends, to give a greater throttle opening, and maintain idle speed.
2. On all applications, the solenoid plunger extends during certain deceleration modes for improved emission control. This action also occurs on A/C equipped vehicles, whether A/C switch is on or off. Specific adjustment procedure is included on the vehicle emission decal.

ELECTRIC CHOKE

Note. This test should be performed when air temperature is 60-80°F (15-27°C).

1. Allow choke to cool to permit full closing of choke valve when throttle is opened slightly. Start engine and time the interval required for choke valve to reach a fully open position. If choke valve does not fully open within 3 1/2 minutes, proceed with test.
2. With engine running, check voltage at choke heater connection. If voltage is about 12-15 volts, replace electric choke unit. If voltage is low or zero, check all wires and connections and repair as required. Power for choke unit is through the oil pressure switch. Ensure switch circuitry is good.
3. If procedure in step 2) does not correct the problem, replace oil pressure switch.

HOT AIR CHOKE

1. Start and warm engine to normal operating temperature. Ensure choke valve fully opens. If valve does not fully open, check choke housing and hot air inlet to determine if sufficient heat is reaching choke coil.
2. If choke housing and/or hot air inlet are cool, check for loss of vacuum to choke housing, restricted heat inlet in choke housing, restricted hot air inlet pipe or hose and restricted manifold choke heat stove passages. Repair or replace as required.

Scheme 2

1. Using a "T" fitting, connect a vacuum gauge in vacuum line from valve to ILC. Connect a vacuum pump to port one of valve. Apply 17.8 in. Hg vacuum to port one and observe gauge. Gauge should read 16.9 in. Hg vacuum within 6-9 seconds. (Scheme 2) (Scheme 2): Location & ID of Differential Vacuum Delay Valve Ports Identify ports for testing procedure.
2. Remove vacuum gauge and "T" fitting. Connect vacuum pump to port 2 and leave port one open. Air should flow through valve when.5 in. Hg vacuum is applied.

VACUUM BREAK

1. If vacuum break has an air bleed hole, plug off during this test procedure. Use Special Tools (J 23738 A or BT 7517) and hand held vacuum pump. Apply 15 in. Hg vacuum to vacuum break.
2. Apply finger pressure to plunger to see if it has moved through full travel. If not, replace vacuum break. If vacuum break does not hold vacuum for at least 20 seconds, replace vacuum break. Replace vacuum break hoses that are cracked, cut or hardened.

DISASSEMBLY

Note. Before performing any service on carburetor, place carburetor on a Holding Fixture (J 9789 118) to prevent damage to throttle valves.

Air Horn

1. Remove ILC or ISS attaching screws, bracket and assembly. Remove upper choke lever from end of choke shaft by removing retaining screw. Rotate upper choke lever to remove choke rod from slot in lever.
2. Remove choke rod from lower lever inside float bowl casting. Remove rod by holding lower lever outward with small screwdriver and twisting rod counterclockwise.
3. Remove secondary metering rods by removing small screw in top of metering rod hanger. Lift up on metering rod hanger until secondary metering rods clear air horn. Metering rods may be disassembled from hanger by rotating ends out of holes in end of hanger.
4. Using a small drift punch, drive pump lever pivot pin (roll pin) inward until pin is against air cleaner locating boss on air horn casting. Disconnect pump rod from pump lever.
5. Remove vacuum hose from primary vacuum break unit and note location for reassembly reference. Remove 11 air horn-to-float bowl screws. Remove 2 countersunk screws located near venturi. CAUTION: Be careful when removing roll pin to avoid damage to pump lever bosses.
6. Remove secondary air baffle deflector (if equipped) from beneath 2 center air horn screws. Remove air horn from float bowl by lifting straight up. Air horn gasket should remain on float bowl. NOTE: Use care not to damage mixture control solenoid connector, TPS adjustment lever, and small tubes protruding from air horn. DO NOT attempt to remove small tubes.
7. Remove primary vacuum break diaphragm. Remove vacuum break from the air valve rod dashpot link, and dashpot link from air valve lever. Using fingers only, remove TPS plunger by pushing plunger up through air horn seal.
8. Remove TPS seal by inverting air horn and remove staking from around seal retainer with a small screwdriver. Remove and discard retainer and seal. Use care removing retainer and seal to prevent damage to air horn casting.
9. Using a punch and small hammer, remove and discard lean mixture screw plug. Further disassembly of air horn assembly is not required for cleaning purposes. Choke valve and choke valve screws, air valve and air valve shaft should not be removed. Instructions for replacing the air valve closing spring and plastic cam are included in service kit. NOTE: It will be necessary to remove air bleed valve before air horn can be immersed in carburetor cleaner.
10. If necessary to replace idle air bleed valve or disassemble air horn for immersion in carburetor cleaner, cover internal bowl vents and air inlets to bleed valve with tape. Drill off rivet heads of bleed valve cover with a 7/64" drill. Drive remainder of rivet out of tower with drift and small hammer.
11. Lift out cover over valve and remove remaining rivet pieces from inside tower. Turn valve counterclockwise and remove from air horn. Remove and discard "O" ring seals from air bleed valve. Air bleed valve is serviced as a complete assembly only.

Float Bowl

1. Remove air horn gasket by lifting off of dowel locating pins. Discard gasket. Remove accelerator pump plunger and return spring from pump well.
2. Using Mixture Solenoid Mixture Tool (J 28696 10 or BT 7928), loosen mixture solenoid adjusting screw. Remove solenoid adjusting screw, solenoid plunger, and plunger stop bracket (rich limit) as an assembly.
3. Remove solenoid connector screw. DO NOT remove plunger return spring or connector wires from solenoid as it is serviced as a complete assembly.
4. Remove plastic insert from over mixture control solenoid. Carefully lift out each metering rod from guide. Ensure the return spring is removed with each rod.
5. Remove and discard rubber gasket from top of solenoid connector. Remove solenoid adjusting screw tension spring from float bowl. Remove float, needle and seat by pulling up on retaining pin. Using Wrench (J 22769 or BT 3006 M) remove needle seat and remove gasket.
6. Remove large mixture control solenoid tension spring from boss on bottom of float bowl located between metering jet guides. Remove the mixture control solenoid.
7. Remove staking holding TPS in bowl. To do so, protect gasket surface by laying a flat piece of metal across casting.
8. Using a small screwdriver, lightly depress and hold TPS down against spring tension. Carefully remove staking from around TPS by prying upward with a small chisel against the metal piece (not bowl casting).
9. Push up from bottom on electrical connector and remove TPS and connector assembly from bowl. Use care not to damage sensor during removal. Remove spring from bottom of TPS well. Remove plastic filler block from float valve.
10. Using Wrench (J 28696 4 or BT 7928), carefully remove primary metering jets. Make sure return spring is removed with each rod. Remove return spring by sliding it off metering rod. DO NOT attempt to remove secondary metering jets.
11. Remove pump discharge check ball retainer. Invert bowl and catch discharge ball as it falls. Remove secondary air baffle, if replacement is necessary. Only remove pump well fill slot baffle, if necessary.
12. Remove hose from secondary (rear) vacuum break. Remove attaching screws and rotate assembly to remove diaphragm rod from slot in plunger.
13. Align a .159" (No. 21) drill on choke cover retaining rivets and drill only enough to remove rivet head. Using a drift and hammer, drive remainder of rivets out of choke housing. Remove 3 retainers, choke cover gasket (hot air type chokes) and choke cover from choke housing. NOTE: DO NOT remove baffle plate from beneath thermostatic coil on choke cover of hot air type chokes.
14. Remove retaining screw and washer from inside choke housing. Slide choke housing from float bowl. On hot air type chokes, remove plastic type seal from vacuum inlet boss of choke housing.
15. Remove secondary throttle valve lock-out lever from float bowl. Remove lower choke lever from inside float bowl cavity by turning float bowl upside down. Remove coil lever retaining screw from end of intermediate choke shaft and remove lever.
16. Slide intermediate choke shaft from choke housing. Remove fast idle cam from intermediate choke shaft. On hot air type chokes, remove and discard cup seal inside choke housing shaft hole.
17. Remove intermediate choke shaft cup seal from float bowl insert. DO NOT remove insert. Invert float bowl to remove lower choke lever from bowl cavity. Remove fuel inlet nut, gasket and filter. Remove 3 throttle body-to-float bowl screws and throttle body.

Throttle Body

1. Remove accelerator pump rod from throttle lever by rotating rod until tang aligns with slot in lever. NOTE: Further disassembly of throttle body is not required for normal cleaning. Throttle valve screws are permanently staked in position. Throttle body is serviced as complete assembly. DO NOT remove mixture screw plugs unless diagnosis indicates the carburetor is cause of poor engine performance or idle mixture needles or throttle body must be replaced.
2. Turn throttle body over, and position on a holding fixture with manifold side up. Make 2 parallel cuts in throttle body using small hacksaw, cutting on each side of idle mixture needle plug. Cuts should reach down to steel plug, but no more than 1/8" beyond locator points. Distance between saw marks will depend upon size of punch used.
3. Place a flat punch at a point near ends of saw marks. Hold punch at 45 degree angle and drive it into throttle body until casting breaks away, exposing steel plug.
4. Hold punch vertically and drive it into steel plug. Then hold punch at 45 degree angle and drive plug out of casting. Repeat process for remaining mixture needle. Using Wrench (J 29030 B or BT 7610B), remove idle mixture needles. Refer to IDLE MIXTURE (BENCH ADJUSTMENT) procedure in this article.

Note. Hardened steel plug will shatter. It is not necessary to remove plug completely. Remove just enough pieces to allow idle mixture adjusting tool to be used to remove mixture screws and springs. Idle mixture screw head has a "double-D" configuration and can also be removed using a piece of 7/32" copper tubing that has been partially flattened.

CLEANING & INSPECTION

1. Use a regular carburetor cleaning solution. Soak components long enough to thoroughly clean all surfaces and passages of foreign matter.
2. DO NOT soak any components containing rubber, leather or plastic. Particularly DO NOT soak air horn with idle air bleed valve installed, electric choke, ISS, ILC, TPS, thermostatic choke cover and coil, vacuum break diaphragms, pump plunger and other such parts.
3. Remove any residue after cleaning by rinsing components in a suitable solvent.
4. Blow out passages with dry compressed air.

REASSEMBLY

Note. Use new gaskets and seals. Make sure that new gaskets fit correctly and that all the holes and slots are punched through and correctly located.

Scheme 3

1. Install new float bowl to throttle body gasket over locating dowels on bottom of float bowl. Install throttle body over dowels on float bowl. Install 3 throttle body mounting screws and tighten securely.
2. Support carburetor with Holding Fixture (C 38886) to avoid throttle plate damage. Install fuel inlet filter spring, a new filter assembly, new gasket, and inlet nut. Tighten nut to 216 INCH lbs. (24 N.m). (Scheme 3): Exploded View of Rochester E4MC & E4ME Carburetor
3. Install new cup seal into insert on side of float bowl for intermediate choke shaft. Lip on cup seal faces outward. Install secondary throttle valve lock-out lever on float bowl boss with recess in lever hole facing inward.
4. Install fast idle cam on intermediate choke shaft with steps on cam facing downward. Carefully install fast idle cam and intermediate choke shaft assembly in choke housing. Install thermostatic coil lever on flats on intermediate choke shaft. Inside thermostatic choke coil lever is properly aligned when both inside and outside levers face toward fuel inlet. See «ADJUSTMENTS»(/pontiac/firebird/iii-1982-1992/remont/testing-diagnostics/#carburetor-rochester-e4mce4me__adjustments) in this article.
5. Install inside lever retaining screw into end of intermediate choke shaft and tighten securely. Install lower inner choke rod lever into cavity in float bowl. See «ADJUSTMENTS»(/pontiac/firebird/iii-1982-1992/remont/testing-diagnostics/#carburetor-rochester-e4mce4me__adjustments) in this article.
6. Install choke housing to bowl, sliding intermediate choke shaft into lever. A pair of needle-nose pliers may be used to hold lower 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. See «ADJUSTMENTS»(/pontiac/firebird/iii-1982-1992/remont/testing-diagnostics/#carburetor-rochester-e4mce4me__adjustments) in this article.
7. Install choke housing retaining screw and washer and tighten securely. If removed, install air baffle in secondary side of float bowl with notches toward the top. Top of baffle must be flush with bowl casting.
8. If removed, install baffle inside of pump well with slot toward bottom. Install pump discharge ball and retainer screw. Tighten retainer screw securely. If removed, carefully install primary main metering jets.
9. Install large mixture control solenoid tension spring over boss on bottom of float bowl. Install needle seat assembly with gasket. To make adjustment easier, carefully bend float arm upward slightly at notch in arm before assembly. See «ADJUSTMENTS»(/pontiac/firebird/iii-1982-1992/remont/testing-diagnostics/#carburetor-rochester-e4mce4me__adjustments) in this article.
10. 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.
11. 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.
12. Perform float adjustment. See «ADJUSTMENTS»(/pontiac/firebird/iii-1982-1992/remont/testing-diagnostics/#carburetor-rochester-e4mce4me__adjustments) in this article. Install feedback solenoid tension spring. Install feedback solenoid. Check that pin on bottom of solenoid is aligned with hole in bottom of bowl.
13. Insert lean mixture screw through hole in solenoid bracket and install screw so that at least the first 6 threads of screw are engaged in bowl. Install Gauge (C 4899) over the left metering jet rod guide and install solenoid plunger. See «ADJUSTMENTS»(/pontiac/firebird/iii-1982-1992/remont/testing-diagnostics/#carburetor-rochester-e4mce4me__adjustments) in this article.
14. Hold plunger against solenoid and turn solenoid screw using Gauge (C 4898) until solenoid plunger contacts gauge. See «ADJUSTMENTS»(/pontiac/firebird/iii-1982-1992/remont/testing-diagnostics/#carburetor-rochester-e4mce4me__adjustments) in this article. Remove solenoid plunger and gauge. Install feedback solenoid attaching screw. Install filler block, metering rod and spring assemblies. NOTE: DO NOT force metering rod into jet. Use extreme care in handling these parts to avoid damage to rods and springs. If metering rods, jets and springs are replaced they must be installed in matched sets.
15. Install pump return spring in pump well. Install pump plunger assembly in pump well. Hold down pump plunger and install air horn gasket. Position gasket over locating pins on float bowl.
16. Hold down on air horn gasket and pump plunger and install feedback solenoid plunger. Check that plunger arms engage top of each metering rod. If feedback solenoid is replaced, solenoid and plunger must be installed as a matched set.

1. Carefully lower air horn assembly onto float bowl. Check that bleed tubes and accelerating well tubes are positioned properly. DO NOT force the air horn assembly onto bowl, but lower it lightly in place.
2. Install secondary air baffle and air horn mounting screws. Tighten all screws evenly and securely. Install air valve rod into slot in lever. Install other end of rod in choke vacuum diaphragm and install vacuum diaphragm.
3. Connect pump link to pump lever and install retainer. Install secondary metering rod hanger and metering rods and tighten screw securely. Work air valves up and down several times to check operation.
4. Connect choke rod into lower choke lever inside bowl cavity. Install choke rod in upper choke lever and install choke lever. Adjust rich mixture stop screw. See «ADJUSTMENTS»(/pontiac/firebird/iii-1982-1992/remont/testing-diagnostics/#carburetor-rochester-e4mce4me__adjustments) in this article.
5. Install plug into access hole for lean mixture screw and using a suitably sized punch, drive plug into air horn so top of plug is even with air horn. Install plug into access hole for rich mixture screw and drive plug into air horn so that plug is 1/16" below air horn surface. NOTE: The lean and rich mixture plugs must be installed to retain the screw setting and to prevent vapor loss.
6. Install idle air bleed valve, choke cover, choke vacuum diaphragm hose and solenoid idle stop. See «ADJUSTMENTS»(/pontiac/firebird/iii-1982-1992/remont/testing-diagnostics/#carburetor-rochester-e4mce4me__adjustments) in this article.

Air Horn Screw Tightening Sequence Screws 1 and 2 are counter sunk next to venturi. Scheme 4

ADJUSTMENTS

Note. For all on-vehicle adjustments not covered in this article, see appropriate TUNE-UP article.

ANGLE GAUGE ADJUSTMENT TOOL

Manufacturer recommends that some carburetor adjustments be performed using Choke Valve Angle Gauge (J 26701). While preparations and actual adjustment may vary with each individual adjustment, the procedure for using the angle gauge to check the choke valve angle remains the same. Use the following procedure to perform adjustments requiring the use of the choke valve angle gauge.

Choke Valve Angle Gauge This gauge must be used to perform some adjustments. Scheme 5

1. With choke valve closed, place angle gauge magnet squarely on choke valve. Rotate degree scale on angle gauge so that zero degree mark is opposite pointer.
2. Rotate leveling bubble on angle gauge until it is centered. Rotate degree scale until specified degree mark is opposite pointer.
3. Place gauge on throttle blade as specified in carburetor adjustment procedures. If bubble is centered, adjustment is correct. If not, adjust carburetor as outlined.

FLOAT LEVEL (WET SETTING)

Note. This is an on-vehicle adjustment.

Scheme 6

1. With engine running at idle and choke valve wide open, carefully insert float gauge into vent slot or vent hole (next to air cleaner mounting stud) in air horn. Allow gauge to float freely. (Scheme 6) NOTE: Pressing down on float gauge could result in float damage or carburetor flooding. (Scheme 6): Wet Float Level Adjustment Allow float gauge to float freely.
2. With gauge floating freely, observe mark on gauge which aligns with top of casting (at eye level). Reading should be within 2/32" (1.58 mm) of specified float level. Incorrect fuel pressure will affect fuel level.
3. If reading is not within 2/32" (1.58 mm) of specified float level, remove carburetor. Remove air horn and perform «FLOAT LEVEL (DRY SETTING)»(/pontiac/firebird/iii-1982-1992/remont/testing-diagnostics/#carburetor-rochester-e4mce4me) adjustment.

Dry Float Level Adjustment. Scheme 7

1. Remove air horn, feedback solenoid plunger, and air horn gasket. Remove plastic float bowl insert. Hold float bowl retainer firmly in place.
2. Push float down lightly against needle. Measure float height from top of casting to top of float at a point 3/16" from end of float. Float level should be within 1/16" of specifications.
3. If float level is too high, hold retainer in place and push down on center of float pontoon to obtain correct setting.
4. If float level is too low, remove metering rods and feedback solenoid connector screw. Count and record for reassembly the number of turns needed to lightly bottom lean mixture screw.
5. Remove feedback solenoid assembly. Bend float upward to adjust. Recheck float level. Reassemble float bowl components. Lightly bottom lean mixture screw, then back out screw to number of turns previously recorded. Reinstall air horn.

SOLENOID LEAN MIXTURE SCREW (BENCH ADJUSTMENT)

Note. This is a preliminary adjustment only. It is required to ensure that lean mixture screw is set close to specifications prior to final adjustment. Final adjustment must be made with carburetor installed and engine running. See appropriate TUNE-UP article.

Solenoid Lean Mixture Screw Bench Adjustment Lean mixture screw should be installed with first 6 threads engaged in float bowl. Courtesy of General Motors Corp. Scheme 8

1. Install plastic aneroid cavity insert beneath mixture control solenoid connector in float bowl (if used). Ensure insert is installed with inset aligned with recess of bowl cavity and seated flush with bowl casting surface. Tang on upper lip of insert goes in deep slot of bowl closest to fuel inlet nut.
2. Install mixture control solenoid screw tension spring between raised bosses next to float hanger pin. Install a new rubber gasket on top of solenoid connector. Install Mixture Control Solenoid Gauge (J 33815 1 or BT 8253 A) over throttle lever side metering jet guide.
3. Carefully install mixture control solenoid and connector in float chamber. Align pin on end of solenoid with hole in raised boss at bottom of bowl. Align connector wires to fit in slot in bowl or plastic insert (if used).
4. Install solenoid lean mixture screw through solenoid rich limit stop bracket, and position plunger so that it slides freely on the stop bracket and through tension spring in float bowl.
5. Align solenoid plunger into solenoid body. Hand thread solenoid adjusting screw to ensure proper installation.
6. Hold solenoid plunger against solenoid stop. Using Lean Mixture Screwdriver (J 28696 10 or BT 7928), slowly turn lean mixture screw clockwise until solenoid plunger just contacts gauging tool. (Scheme 9)
7. Adjustment is correct when solenoid plunger is contacting BOTH the solenoid stop and gauging tool. Remove solenoid plunger and gauging tool.

SOLENOID RICH MIXTURE STOP SCREW (BENCH ADJUSTMENT)

Note. This is a preliminary adjustment only. It is required to ensure that rich mixture stop screw is set close to specifications prior to final adjustment. Most General Motors models use a rich limit stop bracket and there is no adjustment. If equipped with an adjustment screw, final adjustment must be made with carburetor installed and engine running. See appropriate TUNE-UP article.

Solenoid Rich Mixture Stop Screw Bench Adjustment Air horn must be properly installed prior to adjustment. Scheme 9

1. With solenoid lean mixture screw properly set and air horn installed, insert plastic float gauge in vertical "D" shaped vent hole in air horn casting.
2. With float gauge installed, read mark on gauge that lines up with top of air horn casting at eye level. Record reading. Lightly depress float gauge and again read mark on gauge that lines up with top of casting. Record reading.
3. Subtract the 2 readings taken in step 2). This difference is the total solenoid travel. Using a "double D" wrench, turn rich mixture stop screw until total solenoid travel (difference between readings) is 4/32" (3.17 mm). (Scheme 10)
4. After adjustment, install lean mixture screw plug and rich mixture stop screw plug. Plugs must be installed to seal settings and to prevent fuel vapor loss. (Scheme 10)

Installing Lean Mixture Screw Plug & Rich Mixture Stop Screw Plug Plugs seal settings and prevent loss of fuel vapor. Scheme 10

Propane Idle Set

This procedure should only be used if an idle defect still exists after normal diagnosis reveals no other faulty condition such as incorrect basic timing, incorrect idle speed, faulty hose or wiring connections.

1. Remove concealment plugs. Set parking brake and place transmission in neutral. Turn off all lights and accessories. Connect a tachometer to engine. Start engine and allow it to warm up on second highest step of fast idle cam until normal operating temperature is reached. Return engine to idle. Turn off engine.
2. Disconnect and plug vacuum hose at EGR valve and canister purge hose at canister. Disconnect idle solenoid connector. Ground carburetor switch (Black wire). Remove choke vacuum hose from carburetor nipple and install propane supply hose in its place.
3. With propane bottle in upright position and in a safe location, remove PCV valve from valve cover. Allow valve to draw underhood air. Disconnect engine harness lead from oxygen sensor and ground engine harness lead. CAUTION: Care should be used so that no pulling force is put on wire attached to the oxygen sensor. The "bullet" connector to be disconnected is approximately 4" from the sensor.
4. Start and run engine for at least 2 minutes to allow effect of disconnecting oxygen sensor to take place. Open propane main valve. Slowly open propane metering valve until maximum engine RPM is reached. When too much propane is added, engine RPM will decrease. "Fine tune" metering valve to obtain highest rpm.
5. With propane still flowing, adjust idle speed screw on solenoid to achieve specified propane RPM. Again, "fine tune" metering valve to obtain highest engine RPM. If there has been a change in maximum RPM, readjust idle speed screw on solenoid to specified propane RPM.
6. Turn off propane main valve and allow engine speed to stabilize. Slowly adjust idle mixture screws by equal amounts using Special Adjuster (C 4895 or BT 7610 B), pausing between adjustments to allow engine speed to stabilize, to achieve smoothest idle at specified idle RPM.
7. Turn on propane main valve. "Fine tune" metering valve to obtain highest engine RPM. If maximum speed is more than 25 RPM different than specified propane RPM, repeat test steps 4) through 6).
8. Turn off propane main and metering valves. Remove propane supply hose. Reinstall PCV valve. Unplug and reconnect all hoses. Remove jumper wire and reconnect oxygen sensor.
9. After adjustments are complete, seal mixture screws in throttle body using silicone sealant. The sealer is required to discourage unnecessary adjustments of setting and to prevent fuel vapor loss in that area. Perform solenoid idle stop, idle RPM and fast idle adjustments.

Bench Adjustment

Note. This is a preliminary adjustment only. It is required to ensure that mixture screws and idle air bleed valve are set close to specifications prior to final adjustment. Final adjustment must be made with carburetor installed and engine running. See appropriate TUNE-UP article.

1. With concealment plugs removed, use compressed air to remove any metal chips. Lightly seat mixture screws. Back out mixture screw 3 turns.
2. Remove concealment plug. Remove air bleed valve. Discard "O" rings from valve. The air bleed valve is serviced as a complete assembly only.
3. Lightly coat "O" rings with automatic transmission fluid and install on air bleed valve. Install air bleed valve in air horn, ensuring proper thread engagement.
4. To adjust idle air bleed valve, insert Air Bleed Valve Gauging Tool (J 33815 2 or BT 8253 B) in throttle side "D" shaped vent hole in air horn casting. Upper end of tool should be positioned over open cavity next to valve. (Scheme 11)
5. Hold the gauging tool down lightly so solenoid plunger is against solenoid stop. Adjust air bleed valve so gauging tool will pivot over and just contact top of valve. (Scheme 11)

Idle Mixture Bench Adjustment Make final adjustments with carburetor installed and engine running. Scheme 11

LEAN IDLE MIXTURE ADJUSTMENT

1. Lean mixture screw must have at least first 6 threads engaged in float bowl to assure proper installation. Install Gauge (C 4899 or BT 8253 A) over the left metering rod guide and install solenoid plunger.
2. Hold plunger against solenoid and turn lean mixture using Adjuster (C 4898 or BT 7928) until solenoid plunger contacts gauge. Remove gauge and proceed with carburetor reassembly.

ACCELERATOR PUMP ROD

Accelerator pump rod adjustment is not required.

AIR VALVE SPRING

1. Use 3/32" (2.38 mm) Allen wrench to loosen lock screw. Turn tension adjusting screw counterclockwise until air valve opens part way.
2. Turn tension adjusting screw clockwise until air valve just closes. Then turn adjusting screw clockwise specified number of turns. (Scheme 12)
3. Hold adjusting screw and tighten lock screw. Apply lithium base grease to lubricate contact area.

Air Valve Spring Adjustment Apply lithium base grease to lubricate contact area. Scheme 12

CHOKE COIL LEVER

Note. Choke coil cover uses rivets in place of retaining screws. If necessary to remove choke coil cover, see DISASSEMBLY and REASSEMBLY procedures in this article.

1. Remove retaining rivets. Remove choke cover and coil assembly from choke housing. (Scheme 13)
2. Position fast idle speed cam follower on high step of fast idle cam.
3. Push up (counterclockwise) on choke coil tang to close choke valve.
4. Insert.120" (3.0 mm) drill or plug gauge in hole provided in choke housing. Lower edge of choke lever inside housing should just touch drill or plug gauge.
5. To adjust, bend choke rod. (Scheme 14)

Note. Electric choke units do not use a gasket between choke cover and choke housing.

Choke Coil Lever Adjustment Bend choke rod to adjust. Scheme 13

CHOKE ROD (FAST IDLE CAM)

Note. Choke coil lever adjustment must be correct before performing this adjustment. Fast idle speed adjustment must be performed using the Emission Control Tune-Up Decal with carburetor installed and vehicle running. Adjustment is performed with choke valve angle gauge. Refer to the ANGLE GAUGE ADJUSTMENT TOOL procedure at beginning of ADJUSTMENTS. DO NOT remove rivets and choke cover to perform this adjustment.

1. Attach rubber band to Green tang of intermediate choke shaft. Open throttle to allow choke valve to close. Set angle gauge onto choke valve and set to specified angle.
2. Place fast idle speed cam follower on second step of fast idle cam against shoulder of highest step. If cam follower does not contact cam, turn in fast idle speed screw additional turns. (Scheme 14)
3. To adjust, bend tang on fast idle cam until bubble of choke valve angle gauge is centered.

Choke Rod (Fast Idle Cam) Adjustment Bend tang on fast idle cam to adjust. Scheme 14

Front Vacuum Break Adjustment Turn vacuum break adjustment screw to adjust. Scheme 15

PRIMARY (FRONT) VACUUM BREAK

Note. Choke coil lever and choke rod (fast idle cam) adjustments must be correct before performing this adjustment. Adjustment is performed with choke valve angle gauge. See the ANGLE GAUGE ADJUSTMENT TOOL procedure at the beginning of ADJUSTMENTS. DO NOT remove rivets and choke cover to perform this adjustment.

1. Attach rubber band to Green tang of intermediate choke shaft. Open throttle to allow choke valve to close. Set angle gauge onto choke valve and set to specified angle.
2. Using an outside vacuum source of at least 18 in. Hg vacuum, fully retract primary (front) vacuum break diaphragm. If air valve rod restricts vacuum break plunger from retracting, bend rod to allow full plunger travel. Be sure leaf bucking spring is seated against lever (if equipped). (Scheme 15) NOTE: On models equipped with air bleed, remove rubber cover from filter and plug vacuum tube with a piece of tape. If bleed hole is in end of diaphragm, plug hole in end of diaphragm with a piece of tape. Remove tape after completing adjustment.
3. To adjust, turn vacuum break adjustment screw with vacuum still applied. Adjustment is correct when bubble of choke valve angle gauge is centered.

SECONDARY (REAR) VACUUM BREAK

Note. Choke coil lever and choke rod (fast idle cam) adjustments must be correct before performing this adjustment. Adjustment is performed with choke valve angle gauge. See the ANGLE GAUGE ADJUSTMENT TOOL procedure at the beginning of ADJUSTMENTS. DO NOT remove rivets and choke cover to perform this adjustment.

1. Attach rubber band to Green tang of intermediate choke shaft. Open throttle to allow choke valve to close. Set angle gauge onto choke valve and set to specified angle.
2. Using an outside vacuum source of at least 18 in. Hg, fully retract secondary (rear) vacuum break diaphragm. If air valve rod restricts vacuum break plunger from retracting, bend rod to allow full plunger travel. Be sure leaf bucking spring is compressed (if equipped). (Scheme 16) NOTE: On models equipped with air bleed, remove rubber cover from filter and plug vacuum tube with a piece of tape. If bleed hole is in end of diaphragm, plug hole in end of diaphragm with tape. On delay models with air bleed, plug end cover with an accelerator pump plunger cup. Remove tape or cup after completion of the adjustment.
3. To adjust on models equipped with hex adjustment, use a 1/8" hex wrench to turn adjustment screw in rear cover of vacuum break with vacuum still applied. To adjust on models without hex adjustment, support rod at "S" and bend vacuum break rod with vacuum still applied. Adjustment is correct when bubble of choke valve angle gauge is centered.

Secondary (Rear) Vacuum Break Adjustment Turn screw or bend vacuum break rod to adjust. Scheme 16

AIR VALVE ROD - FRONT

1. Using an outside vacuum source of at least 18 in. Hg, fully retract primary (front) vacuum break diaphragm. Plug purge bleed hole (if equipped) with masking tape. Hole is located in end of diaphragm. (Scheme 17)
2. Ensure air valve is completely closed. Measure clearance between rod and end of slot in lever. Insert a.025" drill or plug gauge between rod and end of slot. (Scheme 17)
3. Bend rod at point shown to adjust gauge clearance to.025" with vacuum still applied. Remove tape and reconnect vacuum hose to diaphragm.

Front Air Valve Rod Adjustment Air valve must be completely closed. Scheme 17

AUTOMATIC CHOKE

Note. Choke coil cover is retained in place with rivets. No adjustment is required. If necessary to remove choke coil cover, refer to DISASSEMBLY and REASSEMBLY procedures under OVERHAUL in this article. Remove choke cover only if a major overhaul is required or if the choke cover requires replacement.

CHOKE UNLOADER

Note. Choke coil lever and choke rod (fast idle cam) adjustments must be correct before performing this adjustment. Adjustment is performed with choke valve angle gauge. See the ANGLE GAUGE ADJUSTMENT TOOL procedure at the beginning of ADJUSTMENTS. DO NOT remove rivets and choke cover to perform this adjustment.

1. Attach rubber band to Green tang of intermediate choke shaft. Open throttle to allow choke valve to close. Set angle gauge onto choke valve and set to specified angle.
2. Hold secondary lock-out lever away from pin. (Scheme 18) Hold throttle lever in wide open position.
3. To adjust, bend choke unloader tang of fast idle lever until bubble of choke valve angle gauge is centered. Remove gauge.

Choke Unloader Adjustment Bend tang to adjust. Scheme 18

Lock-Out Lever Side Clearance

1. Hold choke valve and throttle valves completely closed. (Scheme 19)
2. Measure secondary throttle valve lock-out specified side clearance between pin and lock-out lever.
3. Specified lock-out lever side clearance is.015" (.381 mm). To adjust, bend pin.

Secondary Throttle Valve Lock-out Adjustment. Scheme 19

Lock-Out Lever Opening Clearance

1. Push down on tail of fast idle cam to open choke valve completely.
2. Measure secondary throttle valve lock-out specified opening clearance between end of pin and toe of lock-out lever.
3. Specified clearance is .015" (.381 mm). To adjust, file end of lock-out pin. Make sure all burrs are removed.

CARBURETOR ADJUSTMENT SPECIFICATIONS (E4MC)

CARBURETOR ADJUSTMENT SPECIFICATIONS (E4ME)

See also:
• ADJUSTMENTS
• FLOAT LEVEL (DRY SETTING)
• DISASSEMBLY
• REASSEMBLY
• ANGLE GAUGE ADJUSTMENT TOOL