Idle Mixture (Propane Method)

Fig. 1 Carburetor enrichment tool:

This procedure should only be used after normal diagnosis has revealed no other faults, or if carburetor has been overhauled. Idle mixture adjustment requires artificial propane enrichment. A propane enrichment tool, C-4464 or equivalent, Fig. 1, must be used to adjust idle mixture. Before proceeding, make sure that propane cylinder is adequately filled to ensure correct propane flow.

Fig. 2 Propane enrichment specification chart:

HOLLEY 6280 CARBURETOR

1. Remove concealment plug from mixture adjusting screw, refer to ``Carburetor Section.''
2. Set parking brake and place transmission in Neutral position.
3. Turn off all lights and accessories, then connect suitable tachometer.
4. Start engine and allow to reach normal operating temperature, then turn off engine.
5. Disconnect and plug vacuum hose at EGR valve and ESA computer.
6. Disconnect and plug canister purge hose at canister.
7. Ground carburetor switch using suitable jumper wire.
8. Disconnect carburetor electrical connector, then remove the green duty cycle wire and blue idle solenoid wire from the connector. Reconnect carburetor electrical connector less the two removed wires.
9. Start engine and run for approximately 4 minutes.
10. Disconnect vacuum hose from choke diaphragm at the carburetor and install propane supply hose in its place. Ensure propane cylinder remains upright during this procedure.
11. Remove PCV valve from cylinder head cover and allow valve to draw underhood air.
12. Open propane main valve, then slowly open propane metering valve until maximum engine RPM is reached. Too much propane will cause engine speed to drop. Adjust metering valve to obtain maximum idle RPM.
13. With propane still flowing, adjust idle speed screw on solenoid to obtain specified propane RPM, Fig. 2.
14. Adjust metering valve to obtain maximum RPM. If there has been a change in maximum RPM, readjust idle speed screw to specified enriched RPM.
15. Turn off propane valve and allow engine speed to stabilize.
16. Slowly adjust mixture screws by equal amounts to obtain smoothest idle at specified curb idle RPM, allowing time between adjustments for engine speed to stabilize.
17. Turn on main propane valve and adjust metering valve to obtain maximum engine RPM. If maximum engine speed differs by more than 25 RPM from specified propane RPM, repeat steps 12 through 17.
18. When adjustment is correct, turn off both propane valves, stop engine and remove tool.
19. Install concealment plugs and vacuum lines, then connect PCV valve.
20. Disconnect carburetor electrical connector, then install green and blue wires in their correct positions. Reconnect carburetor electrical connector.
21. Perform ``Curb Idle Speed, Adjust'' and ``Fast Idle Speed, Adjust'' procedures.

Fig. 2 Propane enrichment specification chart:

ROCHESTER QUADRAJET CARBURETOR

1. Remove concealment plug from mixture adjusting screw, refer to ``Carburetor Section.''
2. Set parking brake and place transmission in Neutral position.
3. Turn off all lights and accessories, then connect suitable tachometer.
4. Start engine and allow to reach normal operating temperature, then turn off engine.
5. Disconnect and plug vacuum hose at EGR valve and canister purge hose at canister.
6. Disconnect idle solenoid connector, then ground carburetor switch black wire.
7. Remove choke vacuum hose from carburetor nipple, then install propane supply hose in its place. Ensure propane cylinder remains upright during this procedure.
8. Remove PCV valve from valve cover and allow valve to draw underhood air.
9. Disconnect and ground oxygen sensor electrical connector.
10. Start engine and allow to run for approximately 2 minutes.
11. Open propane main valve, then slowly open propane metering valve until maximum engine RPM is reached. Too much propane will cause engine speed to drop. Adjust metering valve to obtain maximum idle RPM.
12. With propane still flowing, adjust idle speed screw on solenoid to obtain specified propane RPM, Fig. 2.
13. Adjust metering valve to obtain maximum RPM. If there has been a change in maximum RPM, readjust idle speed screw to specified enriched RPM.
14. Turn off propane valve and allow engine speed to stabilize.
15. Slowly adjust mixture screws by equal amounts, using tool No. C-4895 or equivalent, obtain smoothest idle at specified curb idle RPM, allowing time between adjustments for engine speed to stabilize.
16. Turn on main propane valve and adjust metering valve to obtain maximum engine RPM. If maximum engine speed differs by more than 25 RPM from specified propane RPM, repeat steps 11 through 16.
17. When adjustment is correct, turn off both propane valves, stop engine and remove tool.
18. Install PCV valve and all vacuum hoses.
19. Remove jumper wire and connect oxygen sensor electrical connector.
20. Install concealment plugs, then perform ``Curb Idle Speed, Adjust'' and ``Fast Idle Speed, Adjust'' procedures.