Idle Mixture (Propane Method)

Concealment Plug Removal:

NOTE: Tampering with the carburetor is a violation of Federal law. Adjustment of the carburetor idle air-fuel mixture can only be performed under certain circumstances such as: If an idle defect exists after normal diagnosis reveals no faulty conditions such as incorrect basic timing, incorrect idle speed, faulty hose or wiring connections, etc. Adjustment can also be performed after a major carburetor overhaul. Upon completion of adjustment, concealment plugs must be replaced.

PROPANE METHOD

1. Remove concealment plugs as follows:
a. Remove air cleaner.
b. Remove vacuum hose from base of carburetor.
c. Center punch mixture screw housing 1/4" from the end of the housing of each mixture screw.
d. Using a 3/16" drill bit, drill through both housings on previously punched mark.
e. Using a small drift punch, pry concealment plugs from housing and save for reuse.

2. Set parking brake and place transmission in neutral position.
3. Turn off all lights and accessories.
4. Connect a tachometer to the engine.
5. Start the engine and allow to warm up while idling on second highest step of high idle cam. Once engine is warmed up, return to idle and turn engine off.
6. Disconnect and plug vacuum hoses from EGR valve and Electronic Spark Advance (ESA) computer.
7. Disconnect and plug hose from purge canister at canister.
8. Ground carburetor idle ground switch with a suitable jumper wire.
9. Disconnect carburetor electrical connector from engine wiring harness, and remove the green duty cycle wire and the blue idle solenoid wire from the connector. Connect carburetor electrical connector less the two removed wires.
10. Start engine and allow to idle for at least 4 minutes.

Propane Supply Tool:

11. Disconnect vacuum supply hose from choke diaphragm at the carburetor, and tee a propane supply in its place. Make sure all vacuum hoses are reconnected, and that the propane bottle remains upright throughout the procedure.
12. Remove PCV valve from valve cover and allow valve to draw underhood air.
13. Open the main valve on the propane bottle, then slowly open the metering valve until maximum engine RPM is reached.
NOTE:Too much propane will cause RPM to drop. Adjust metering valve to obtain maximum idle RPM.
14. With propane still flowing, adjust idle sped screw on solenoid to specifications. Adjust the propane metering valve to obtain maximum RPM. If there has been a change in maximum RPM, readjust the idle speed screw to the specified propane RPM.
15. Turn off propane main valve and allow engine speed to stabilize.
16. Slowly adjust mixture screws by equal amounts to obtain smoothest idle at specified curb idle RPM. Allow 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 from specified propane RPM by more than 25 RPM, repeat steps 13 through 17.
18. When adjustment is correct, turn off both propane valves, stop engine and remove tool.
19. Install concealment plugs and vacuum lines, and reconnect PCV valve.
20. Disconnect carburetor electrical connector, and reinstall blue and green wires in their respective positions. Connect carburetor electrical connector.
21. Perform "Curb Idle Speed Adjustment" and "Fast Idle Speed Adjustment" procedures.