Carburetor - Keihin 2-bbl Honda Civic III

DESCRIPTION

Carburetor is a 2-barrel downdraft design incorporating electronic and automatic compensating devices to maintain proper air/fuel mixture under all operating conditions. The fuel flow from the pump is regulated by a temperature sensitive by-pass valve within the carburetor. When cold, by-pass valve is closed so the accelerator pump receives maximum fuel. When engine is warm, by-pass valve opens and allows excess fuel back into float chamber.

Carburetor components include an electrically-heated automatic choke, choke opener diaphragm, throttle controller diaphragm, idle controller diaphragm (A/C), dashpot diaphragm, fuel cut-off valve, primary slow mixture cut-off solenoid valve, fast idle unloader, power valve, air vent cut-off diaphragm, air temperature sensor, intake air control diaphragm and air jet controller (all except Federal 1.3L models).

The Air Jet Controller (AJC) is an atmospheric pressure sensing device, controlling the amount of air flow into slow and main air jets of primary carburetor throat and slow air jet of secondary carburetor throat. As outside pressure is reduced by increasing altitude, the bellows expand to open valve in AJC, increasing air flow to the jets to maintain optimum air/fuel mixture.

Both choke valve setting and fast idle position are controlled during engine warm-up by automatic choke. It consists of the choke valve with its linkage, choke heater electrical circuit, choke opener, fast idle and fast idle unloader system.

A heat riser, utilizing engine coolant, is built into intake manifold to prevent carburetor icing and improve cold driveability, thus improving air/fuel mixture atomization. A by-pass valve, with thermostat, shuts off coolant flow at normal operating temperatures.

All models are equipped with a power valve. The 1.3L and 1.5L HF engine power valve is open when intake air temperature is below 59°F (15°C), or when vehicle is going slower than 10 MPH and intake air temperature is above 59°F (15°C). When vehicle exceeds 10 MPH, power valve is controlled by vacuum switch signal to power valve solenoid valve. The power valve solenoid valve is energized by low manifold vacuum switch.

On other 1.5L engines, the control unit energizes power solenoid valve solenoid to cut off manifold vacuum to power valve which supplies supplementary fuel to primary main fuel passage. The power valve control solenoid valve is on when coolant temperature is above 149°F (65°C) and engine speed is below 2800-3300, and when intake air temperature is below 60°F (15°C) or coolant temperature is below 65°F (65°C) and vehicle speed is below 10 MPH or when engine speed is above 2800-3300 RPM and vacuum switch B is off.

CARBURETOR MODEL IDENTIFICATION

ADJUSTMENTS

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

Choke Coil Tension & Linkage

1. Ensure engine is cold. Remove air cleaner. Open and close throttle fully to close choke valve. The choke valve should close completely. If temperature is above 82°F (28°C), choke will not close completely but should be open less than .125" (3 mm).
2. If choke valve closes properly, proceed to FAST IDLE UNLOADER (COLD ENGINE) in TESTING section. If choke valve does not close, spray linkage with carburetor cleaner and recheck choke.
3. If choke still fails to close properly, drill out cover retaining rivets using a .156" (4.10 mm) drill bit. Remove choke cover. CAUTION: Cover the carburetor with a clean shop towel to prevent chips from falling into carburetor throat during drilling operation.
4. Inspect linkage for free movement. Repair or replace parts as necessary. Reinstall cover and adjust so index marks align. Secure cover with new rivets. Recheck choke valve clearance. If choke still does not close properly, replace cover. Reinstall air cleaner.

Choke Opener

1. Disconnect choke heater wire. Open and close throttle fully to close choke valve. Start engine and note if choke valve opens slightly. If choke opens, go to step 5) or 8), depending on coolant temperature.
2. If choke does not open, check linkage for free movement, repair as needed and recheck choke. If choke still does not open, check choke opener diaphragm. Remove 2 mount screws. Attach a hand vacuum pump (A973X-041-XXXXX) to diaphragm hose fitting.
3. Hold finger over orifice in opener, while drawing enough vacuum to pull opener rod all the way in; then stop. If the rod will not stay in, replace the opener.
4. If the rod stays in, check vacuum port in carburetor and clean it out if necessary. If clean, check CRANKING LEAK SYSTEM in TESTING section of this article. After replacing or reinstalling choke opener, recheck opener operation and adjust linkage as necessary. See CHOKE OPENER LINKAGE.
5. If engine coolant temperature is less than 52°F (11°C), tab "A" on choke opener lever should not be seated against carburetor stop. (Scheme 73) If tab "A" is not seated, go to step 8).
6. If tab "A" is seated, disconnect choke opener hose. If tab "A" comes off its seat, check vacuum line No. 18 to thermovalve "B" for blockage and check that thermovalve "B" is open.
7. If tab "A" does not come off its seat, press down on choke opener lever until it does. If it won't stay off, clean out choke opener fitting with a No. 76 (.5 mm) drill bit and recheck. If tab "A" still does not come off its seat, replace choke opener.
8. If coolant temperature is more than 66°F (19°C), tab "A" on choke opener lever should be seated against carburetor stop. (Scheme 73) If tab "A" is seated, reconnect choke heater wire and proceed to CHOKE COIL HEATER in TESTING section of this article.
9. If tab "A" is not seated, check vacuum line No. 18 to thermovalve "B" for leaks and check that thermovalve "B" is closed.

Checking Choke Opener Lever Position. Scheme 73

Note. Choke opener linkage check and adjustment is not necessary unless linkage has been bent, choke opener replaced or the vehicle has poor cold starting. The linkage check may be made with engine hot or cold.

Choke Opener Linkage

1. Remove choke cover. While holding the choke valve closed, open and close the throttle fully to engage the choke and fast idle linkage.
2. Disconnect the choke opener hose from the steel tubing manifold and attach a check valve. (Scheme 74) Apply 15-85 psi (1-6 kg/cm 2 ) compressed air to choke opener to hold its bleeder valve closed.
3. Push choke opener lever toward opener diaphragm until it stops (opener rod seats against pressurized bleed valve). Pull choke drive lever down against choke opener lever to take all free play out of linkage.
4. Measure clearance between choke valve and carburetor body. If necessary, adjust first stage clearance specification to.054-.060" (1.37-1.51 mm) for 1.5L or.044-.050" (1.12-1.26 mm) for 1.3L and 1.5L HF, by bending tab "D". (Scheme 74)
5. Remove the check valve and reconnect choke opener hose. Hold both levers together. Push levers toward opener diaphragm until tab "A" seats against carburetor. Measure choke valve clearance.
6. If necessary, adjust second stage clearance to.075-.083" (1.91-2.09 mm) for all engines, by bending tab "A". (Scheme 74) While still holding choke opener lever tab "A" against its seat, release choke drive lever and measure choke valve clearance.
7. Tab "C" on the drive lever should stay seated against the spring loop. If not, hold choke valve closed, open and close throttle to engage choke and fast idle linkage and recheck.
8. If necessary, adjust third stage clearance specification to.201-.219" (5.04-5.52 mm) for 1.5L or.070-.250" (3.70-4.18 mm) for 1.3L and 1.5L HF, by bending tab "C". (Scheme 74)

Adjusting Choke Opener Linkage. Scheme 74

Scheme 75

1. Ensure vehicle is on level ground. Start engine and warm to normal operating temperature. Snap throttle between idle and 3000 RPM several times and then let engine idle.
2. When fuel level stabilizes, check that it is centered in the inspection window. If fuel level is higher or lower than mark, adjust by turning the external adjusting screw. (Scheme 75) (Scheme 75): Checking and Adjusting Float Level
3. When correct float level is achieved, paint adjusting screw with White paint to aid visual inspection of adjustment screw location and to help prevent adjustment from changing.

THROTTLE CABLE

1. Check throttle cable for smooth operation, with no binding or sticking. Repair or replace throttle cable as necessary. Check for cable free play (deflection) at linkage.
2. Standard cable deflection (side-to-side) is 3/16-3/8". If necessary, adjust deflection by loosening lock nut and turning adjusting nut.
3. After adjustment, securely tighten lock nut. Ensure throttle valve opens fully when accelerator pedal is depressed and returns to idle position when pedal is released.

FAST IDLE

1. With engine stopped, attach tachometer. Disconnect and plug the inside vacuum hose of the fast idle unloader.
2. Engage fast idle cam by opening and closing throttle fully while holding choke valve closed. Start engine. The fast idle should be within 2500-3500 RPM.
3. If not to specification, reset fast idle by turning fast idle adjusting screw, behind fast idle unloader, on carburetor. Reconnect vacuum hose and detach tachometer.

REDUCED EMISSION ADJUSTMENT (HIGH ALTITUDE)

Note. Any low-altitude 1.3L and 1.5L HF Civic (Federal only) that is normally driven at high altitude (above 4000 ft.) must have the reduced emission adjustment performed. DO NOT adjust any 1.3L vehicles originally sold at high altitude or Calif. spec. vehicles. The models with 1.5L engines may be used at any altitude without additional adjustments.

1. Remove air cleaner. Disconnect all vacuum lines from carburetor. Pull throttle cable out of its bracket. Remove carburetor mount nuts with washers and bolt securing steel tubing vacuum manifold. Lift carburetor clear of its studs.
2. Tilt carburetor backwards so that the throttle controller bracket mount screw may be removed. Remove 2 throttle controller bracket mount bolts, throttle controller bracket and mixture screw cap from carburetor.
3. To set high altitude adjustment, turn mixture screw 1/2 turn clockwise, resulting in no less than 1 full turn from the seated position. Reinstall throttle controller bracket, bolts and screw.
4. Place mixture screw plug back into carburetor. Reinstall carburetor, throttle cable, vacuum hoses and air cleaner. Start engine and warm to operating temperature (cooling fan comes on).
5. Check idle speed with headlights, heater blower, radiator fan and air conditioner (A/C) off. Standard idle speed (in Neutral) for 4-speed manual transmission is 600-700 RPM and 550-650 RPM for 5-speed transmission.
6. Check idle controller boosted speed, on manual transmission vehicles, with headlights on and heater blower set to III. Idle speed should be 600-700 RPM.
7. Turn on the A/C and recheck idle speed. Idle speed should now be 700-800 RPM. If idle speed changes, adjust idle controller as necessary. After adjustment, apply emission control information update label to underside of hood.

CHOKE COIL HEATER

1. Start engine. As engine reaches normal operating temperature, choke valve should fully open. If choke opens completely, proceed to FAST IDLE UNLOADER (HOT ENGINE). If it does not, inspect choke linkage and clean and repair as necessary.
2. If choke still does not open completely, disconnect choke cover wire (White/Blue) from engine compartment wiring harness and check for voltage. There should be battery voltage with the engine running.
3. If there is no voltage, check for an open circuit in the wire (White/Blue) between choke cover connector and voltage regulator connector, or in charge warning light circuit.

CRANKING LEAK SYSTEM

1. Disconnect lower vacuum hose number 28 from the choke opener. Using a vacuum pump, attach pump to end of hose. Operate pump and ensure vacuum remains steady.
2. If vacuum drops, check for leaking hoses. If not found, replace cranking leak solenoid valve and recheck. If vacuum remained as in step 1) turn ignition switch to "START" position. If vacuum releases, system is okay.
3. If vacuum does not release, check for voltage at the cranking solenoid valve connector (Blue/White wire) of control box number 1. If no voltage is present, check wiring and fuse. If voltage is present, check vacuum hose number 28 for blockage or replace cranking solenoid valve and retest.

Cold Engine

1. With engine off, disconnect 2 vacuum hoses from fast idle unloader. Open and close throttle fully to engage fast idle cam. Start engine. Engine should run at fast idle.
2. If engine runs at fast idle, connect a hand vacuum pump (A973X-041-XXXXX) to inside fitting of unloader and draw vacuum. The fast idle speed should drop. If idle speed drops, proceed to FAST IDLE UNLOADER (HOT ENGINE).
3. If engine fails to run at fast idle, stop engine and remove choke cover. Check operation of fast idle cam and repair or replace as necessary.
4. If idle fails to drop, check unloader for leaks, blockage or damaged diaphragm. Remove choke cover. Check unloader rod for free movement. Repair or replace as necessary. Reconnect vacuum hoses.

Hot Engine

1. Warm engine to normal operating temperature. Do not manually open throttle. If speed drops below 1400 RPM, as engine warms, adjust fast idle speed. NOTE: When engine warms up, speed should drop below 1400 RPM as unloader pulls internal choke linkage off fast idle cam.
2. If fast idle does not drop below 1400 RPM, disconnect 2 unloader hoses and check for vacuum. If vacuum is present, check unloader diaphragm for leaks and/or blockage.
3. Remove choke cover and check for free movement of unloader rod. Repair or replace as necessary and retest. If no vacuum is present at the inner fitting, check for vacuum at choke opener and thermovalve B or E. If there is no vacuum at outer fitting, check thermovalve A or D. Repair or replace as necessary.

INTAKE AIR TEMPERATURE SENSOR

1. Disconnect intake air sensor connector. Check continuity across terminals of connector. The sensor should not have continuity if air temperature is more than 73°F (23°C).
2. The sensor should have continuity if air temperature is lower than 40°F (4.5°C). Replace intake air temperature sensor if not as specified.

PRIMARY SLOW MIXTURE CUT-OFF SOLENOID VALVE

Note. The primary slow mixture cut-off solenoid valve blocks fuel to primary idle circuit when engine is shut off.

1. If engine idle is rough or erratic, primary slow mixture cut-off solenoid valve may be malfunctioning. Remove primary cut-off valve and wipe up any spilled fuel before testing.
2. Ground valve (as far from carburetor as possible). Turn on ignition key while watching valve needle. If needle retracts, valve is good. Inspect valve seat and carburetor passage for blockage.
3. If needle does not retract, check for voltage at the solenoid. If voltage is present, check the fuse and wiring.

Exploded View of Choke Assembly, Cut-Off Valve & Diaphragms. Scheme 76

Note. Legend in (Scheme 91) describes components & connections marked w/numbers.

Vacuum Diagram for 1.3L Calif. & Federal Man. & Auto. Trans.). Scheme 77

Vacuum Diagram for 1.3L High Altitude Man. & Auto. Trans. Scheme 78

Vacuum Diagram for 1.5L HF Civic Federal Man. Trans. Only. Scheme 79

Vacuum Diagram for 1.5L HF Calif. Man. Trans. Scheme 80

Vacuum Diagram for 1.5L HF High Altitude. Scheme 81

Vacuum Diagram for 1.5L Federal & High Altitude Man. Trans. Scheme 82

Vacuum Diagram for 1.5L Calif. M/T & A/T w/Man Steer. Scheme 83

Vacuum Diagram for 1.5L Auto. Trans. with Power Steering. Scheme 84

POWER VALVE

Note. The power valve opens as vacuum is reduced and supplies supplementary fuel into main fuel passage when vehicle is in power mode (under acceleration).

1.3L & 1.5L HF

1. Disconnect vacuum hose from power valve. Connect a hand vacuum pump (A973X-041-XXXXX) to the valve. Draw vacuum and listen for a clicking noise from the power valve. If no noise is heard, replace carburetor and retest.
2. If clicking noise is heard, start engine and warm to operating temperature. Disconnect vacuum hose from power valve and connect vacuum gauge to hose. Vacuum should not be available. If vacuum is not available, go to step 4).
3. If vacuum is available, check for voltage at power valve control solenoid valve (Yellow/Black wire), in emission control box number 1 (number 2 for Federal 1.5L HF). If there is voltage, replace power valve control solenoid valve and retest. If there is no voltage, check fuse, wiring and speed sensor, then retest.
4. If vacuum is not available, jack up vehicle, support securely, block rear wheel and set hand brake. Place transmission in 2nd gear. Check for vacuum, at power valve (hose No. 14), above 10 MPH. There should be vacuum.
5. If there is no vacuum, check for voltage at power valve control solenoid valve. If there is voltage, replace vacuum switch B and retest. If there is no voltage, replace power valve control solenoid valve and retest.
6. If there is vacuum (with vehicle still in gear and above 10 MPH), disconnect vacuum hose No. 12 from vacuum pipe manifold to simulate engine load. Vacuum to power valve (hose No. 14) should disappear.
7. If vacuum disappears, system is okay. Reconnect vacuum hoses. The test is complete. If vacuum does not disappear, check for voltage across vacuum switch B with vehicle above 10 MPH.
8. If there is no voltage, check fuses, wiring and speed sensor. If there is voltage, remove control box cover and check for continuity between vacuum switch B wire terminal with hose number 12 (number 1 for Federal 1.5L HF) disconnected.
9. If there is continuity, replace power valve control solenoid valve and retest. If there is no continuity, replace vacuum switch B and retest.

Civic Power Valve Assembly (1.3L & 1.5L HF). Scheme 85

Note. When testing 1.5L (except 1.5L HF) power valve, ensure engine temperature is less than 149°F (65°C).

1.5L (Except 1.5L HF)

1. Disconnect vacuum hose from power valve. Connect a hand vacuum pump (A973X-041-XXXXX) to power valve. Draw vacuum and listen for clicking noise from power valve. If no noise is heard, replace carburetor and retest.
2. If clicking noise is heard, start engine, disconnect vacuum hose from power valve and connect a vacuum gauge to hose. Vacuum should not be available. If vacuum is not available, test is complete.
3. If vacuum is available, check for voltage between connector with positive wire (Blue/Yellow) and connector with negative ground (Black) at power valve control solenoid valve in emission control box.
4. If there is voltage, replace power valve control solenoid valve and retest. If there is no voltage, check for voltage at Blue and Black/Yellow wires of control unit. Check for a good ground between Brown/Black wire of control unit. Replace or repair any problems and retest.
5. If there is no voltage check speed sensor, air temperature sensor, vacuum switch B and thermosensor B in the control unit of Feedback Carburetor System.

Power Valve Assembly (1.5L). Scheme 86

Note. Legend in (Scheme 91) describes components & connections marked w/numbers.

Vacuum and Electrical Connections (1.3L 50 State). Scheme 87

Vacuum and Electrical Connections (1.5L HF Federal). Scheme 88

Vacuum and Electrical Connections (1.5L HF California). Scheme 89

Vacuum and Electrical Connections (1.5L HF High Altitude). Scheme 90

Note. Legend in (Scheme 91) applies to Figures. 5, 6, 7, 8, 9, 10, 11, 12, 15, 16, 17, 18, 19.

Vacuum and Electrical Connections (1.5L Man. & Auto. Trans.). Scheme 91

See also:
• TESTING