Idle Mixture (Propane Method)

Fig. 10 Typical propane 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. 10, must be used to adjust idle mixture. Before proceeding, make sure that propane cylinder is adequately filled to insure correct propane flow.

Fig. 11 Propane enrichment specification chart:

Fig. 12 Adjusting idle mixture. Holley carburetor:

HOLLEY CARBURETORS

1. Remove concealment plug from throttle body, if equipped. Refer to ``Carburetor Section.''
2. Turn off all lights and accessories, then connect tachometer.
3. Start engine and allow to reach normal operating temperature.
4. Disconnect and plug vacuum connector from CCEGR/CVSCC.
5. Disconnect air cleaner heated air door hose from connector and install hose from propane tool metering valve on fitting. Keep propane cylinder in upright position.
6. Disconnect radiator fan electrical connector, then install jumper wire so fan will run continuously.
7. Remove PCV valve and allow valve to draw underhood air, then disconnect kicker solenoid electrical connector, if equipped with 1986-87 4-135 engine.
8. Connect jumper wire between carburetor switch and ground, then disconnect oxygen sensor test connector located on left fender shield, if equipped.
9. Open main propane valve fully, then with air cleaner in position, slowly open propane metering valve until maximum idle RPM is obtained. Too much propane will cause engine speed to drop. Adjust metering valve to obtain maximum idle RPM.
10. With propane still flowing, adjust idle speed screw to get specified RPM, Fig. 11. ``Fine Tune'' propane metering valve to get highest engine RPM. If there had been a change in maximum RPM, readjust idle speed to specified propane RPM, Fig. 12.
11. Turn off main propane valve and allow engine speed to stabilize.
12. Adjust idle mixture screw in small increments to obtain specified curb idle speed, allowing time between adjustments for engine speed to stabilize.
13. Open main propane valve fully, then ``fine tune'' propane metering valve to obtain maximum idle RPM.
14. If engine speed is more than 25 RPM from specified enriched RPM, repeat steps 10-15. When adjustment is correct, turn off both propane valves.
15. Stop engine. Remove propane tool and reconnect vacuum hoses to proper fittings.
16. Install concealment plug, then perform ``Fast Idle Speed, Adjust'' procedure.

Fig. 6 Idle-up adjustment. Mikuni carburetor:

Fig. 11 Propane enrichment specification chart:

Fig. 13 Adjusting idle mixture. Mikuni carburetor:

MIKUNI CARBURETOR

1. Set parking brake and place transaxle in Neutral position, then remove concealment plug from throttle body. Refer to ``Carburetor Section.''
2. Turn off all lights and accessories, then connect tachometer.
3. Start engine and allow to reach normal operating temperature.
4. Disconnect cooling fan electrical connector.
5. Allow engine to run at 2500 RPM for 10 seconds, then return to idle.
6. Remove air cleaner fresh air duct, then install propane supply hose from propane bottle into air cleaner snorkel. Ensure bottle is in the upright position.
7. Open main propane valve fully, then slowly open propane metering valve until maximum idle RPM is obtained. Too much propane will cause engine speed to drop. Adjust metering valve to obtain maximum idle RPM.
8. Note engine RPM increase. On 1984 models, engine RPM should increase 50-65 RPM over curb idle speed and on 1985 models, engine RPM should increase 40-90 RPM over curb idle speed. If enriched RPM is not as specified, proceed to step 9.
9. Adjust propane metering valve to obtain highest engine RPM. With propane still flowing, adjust idle speed screw to obtain specified enriched RPM, Fig. 11.
10. Turn off main propane valve and allow engine speed to stabilize.
11. Adjust idle mixture screw in small increments to obtain specified curb idle speed, Fig. 13, allowing time between adjustments for engine speed to stabilize.
12. Turn on main propane valve, then adjust metering valve to obtain highest engine RPM. If maximum engine speed differs by more than 25 RPM from specified enriched RPM, repeat steps 7 through 12.
13. Turn off both propane valves, then remove propane supply hose and install fresh air duct to air cleaner.
14. Install concealment plug.
15. On vehicles equipped with A/C, set temperature control lever to coldest position and turn on A/C.
16. Set engine speed to 900 RPM by turning idle-up screw, Fig. 6. Ensure A/C compressor is operating during adjustment.
17. On all models, perform ``Fast Idle Speed, Adjust'' procedure.