Fuel Delivery and Air Induction: Adjustments

C-4 System
The Computer Controlled Catalytic Converter (C-4) system provides precise control of air/fuel mixtures during all ranges of engine operation. Because of this system control, special carburetor adjustment procedures are required. Mixture control adjustments should only be performed after carburetor overhaul, or if "Systems Performance Check", outlined previously, indicates the carburetor as source of complaint.

Procedures must be followed in exact sequence to insure correct mixture adjustment. Plugs sealing adjustments should only be removed as specified in procedures. Refer to Concealment Plug Removal, under Carburetor, Service and Repair to remove plugs sealing idle mixture adjusting screws.

Mixture Control (MC) Solenoid Check

Fig. 119 Checking Mixture Control (MC) Solenoid Travel. (Typical):

Before proceeding, modify float gauge, J9789-130 or equivalent, as needed, to fit in vertical "D" shaped vent on carburetor air horn--Fig 119. Gauge must enter hole freely, without binding or sticking.

1. Insert gauge in vent, press down on gauge and release.
2. With gauge released (MC solenoid up position), read gauge at eye level and record reading that lines up with top of air horn casting.
3. Press down lightly on gauge until bottomed (MC solenoid down position). Record reading that lines up with top of air horn casting.
4. Subtract reading in step 2 from reading in step 3 to obtain total MC solenoid travel.
5. If travel is 2/23 to 1/32 of an inch, proceed to "Idle Bleed Valve Adjustment". If travel is not within specifications, proceed to "MC Solenoid Adjustment".

MC Solenoid Adjustment
1. Remove carburetor air horn.
2. Turn MC solenoid screw in float bowl clockwise until lightly seated, counting number of turns necessary.
3. If solenoid screw was 1 1/2-2 1/2 turns out (1979), 3 1/2-3 3/4 turns out (1980 2 Bbl.), or 3 1/2-4 1/2 turns out (1980 4 Bbl.), return screw to previous position and proceed to step 6.
4. If solenoid screw was not within specified range, back screw out 2 turns (1979), 3 3/4 turns (1980 2 Bbl.), or 4 turns (1980 4 Bbl.).
5. Temporarily install air horn and recheck MC solenoid travel. If travel is within specifications, complete air horn installation and proceed to "Idle Bleed Valve Adjustment". If travel is not within specifications, remove air horn.
6. Invert air horn and remove solenoid rich mixture stop screw.
7. Drive out plug located between "D" shaped holes to gain access to stop screw for adjustment.
8. Reinstall solenoid stop screw, turning screw in until lightly seated, then reinstall air horn using a new gasket.
9. Repeat "MC Solenoid Check," using solenoid stop screw to adjust MC solenoid travel to 4/22 inch. Proceed to "Idle Bleed Valve Adjustment".

Idle Air Bleed Valve Adjustment
1. Connect dwell meter to test lead in MC solenoid harness and set meter on 6 cylinder scale. Connect tachometer to engine following manufacturer's instructions.
2. Disconnect and plug purge hose at vapor canister and other hoses as directed by underhood Emission Control Information Label.
3. Start engine and run at idle until it reaches normal operating temperature.

NOTE: It is essential that coolant temperature and oxygen sensors be at operating temperature before proceeding with adjustments. Signals from these.sensors affect dwell readings used to perform adjustments.

4. Place transmission in drive (manual transmission in neutral) and adjust curb idle speed to specifications with throttle stop screw. Observe dwell meter.
5. If dwell reading fluctuates within 25°-35° range, mixture adjustment is correct. Proceed to "A/C Idle Speed Adjustment".
6. If dwell reading does not fluctuate, or if reading is not within 10°-50° range, stop engine and remove cover from idle air bleed valve.

Fig. 120 Mixture Control Solenoid Adjustment Cover Removal. (Typical):

7. On 1979 models, remove staking from around bleed valve cover--Fig 120--remove and discard cover.
8. On 1980 models, remove cover as follows:
a. Cover carburetor air intake, vents, etc. to prevent metal chips from entering engine.

Fig. 121 Idle Air Bleed Valve Cover Removal (Typical):

b. Carefully align a No. 35 drill (.110 inch) on center of rivet securing cover, and drill just enough to remove rivet head--Fig 121. Repeat with remaining rivet.
c. Use a small drift to drive remainder of rivets out of air bleed tower.
d. Remove and discard cover, then remove remainder of rivets from bleed valve cavity.
e. Using compressed air, blow out any dirt or metal chips that may have entered air bleed valve cavity.

9. Start engine and place transmission in drive (manual transmission in neutral).
10. With engine at normal operating temperature, running at specified curb idle speed, adjust air bleed valve to obtain a fluctuating dwell reading within 25°-35° range.
11. With dwell reading within specifications, adjust curb idle speed to specifications, then refer to "A/C Solenoid" if equipped.
12. If unable to obtain specified dwell reading, proceed to "Idle Mixture Screw Adjustment".

Idle Mixture Screw Adjustment
1. Remove plugs sealing mixture screws as outlined in Concealment Plug Removal, under Carburetor, Service and Repair.
2. Reinstall carburetor with air cleaner off and hoses indicated on emissions label disconnected and plugged.

Fig. 122 Idle Mixture Screw Base Adjustment Position.:

3. Turn each mixture screw in until lightly seated, then back screws out specified number of turns--Fig 122. Repeat "Idle Air Bleed Valve Adjustment", as needed to obtain a fluctuating dwell reading within 25°-35° range.
4. If unable to obtain specified reading:
a. If reading is below 25°, turn each mixture screw counter-clockwise 1 full turn.
b. If reading is above 35°, turn each mixture screw clockwise 1 full turn.
5. Repeat "Idle air Bleed Valve Adjustment", as needed to obtain specified dwell reading.

NOTE: If unable to obtain specified dwell reading, check for a defective carburetor idle circuit, and refer to "System Performance Check", outlined previously.

6. Adjust curb idle speed to specifications with throttle stop screw.
7. Stop engine. Reconnect vacuum hoses to proper fittings and install air cleaner.

A/C Solenoid Adjustment
1. Disconnect and plug vacuum hoses as directed on Emission Control Information Label.
2. Connect tachometer to engine. With engine at normal operating temperature, place transmission in drive (manual transmission in neutral).
3. Adjust curb idle speed to specifications with throttle stop screw.
4. Disconnect wiring harness connector to A/C compressor and place A/C control in on position.
5. Momentarily open throttle to allow solenoid plunger to extend, then adjust A/C idle speed to specifications with solenoid plunger screw.
6. Turn off A/C and reconnect wiring harness connector to compressor.
7. Stop engine. Reconnect vacuum hoses to proper fittings.