Idle Mixture (Propane Method)

Fig. 1 Propane enrichment specification chart:

EXC. 1985 MODELS
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, must be used to adjust idle mixture. Before proceeding, make sure that propane cylinder is adequately filled to ensure correct propane flow.
1. Remove concealment plug or limiter cap from mixture adjusting screw. Refer to appropriate carburetor section.
2. Set parking brake and place transmission in Neutral position.
3. Turn off all lights and accessories, then connect tachometer.
4. Start engine and allow to reach normal operating temperature.
5. Disconnect and plug vacuum hose at EGR valve, ESA computer and distributor, as required.
6. On models equipped with carburetor ground switch, connect jumper wire between switch and ground.
7. On models not equipped with Spark Control Computer (SCC), disconnect and plug vacuum hose from carburetor at heated air temperature sensor and OSAC valve, if equipped, then remove air cleaner.
8. On models with SCC, air cleaner cannot be removed but may be propped up.
9. Disconnect vacuum hose from heated air door or choke diaphragm, except as listed below, and connect hose from metering valve on enrichment tool to fitting.
10. Remove PCV valve from cylinder head cover and allow to draw underhood air.
11. Disconnect plug control hose at canister.
12. On models equipped with oxygen sensor feedback, disconnect electrical connector from oxygen sensor and ground connector. Remove and plug vacuum hose at vacuum transducer on SCC, then install suitable vacuum pump to vacuum transducer, apply 16 inches of vacuum, and allow engine to run for two minutes.
13. On models without oxygen sensor feedback, allow engine to run for one minute.
14. On all models, open main propane valve fully. 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.
15. With propane flowing, adjust idle speed to specified enriched RPM, Fig. 1, by turning idle speed screw.
16. Adjust metering valve to obtain maximum RPM. If there has been a change in maximum RPM, readjust idle speed screw to specified enriched RPM.
17. Turn off main propane valve and allow engine speed to stabilize.
18. Adjust mixture screws to obtain smoothest idle at specified curb idle RPM, allowing time between adjustments for engine speed to stabilize.
19. 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 enriched RPM, repeat steps 15 through 20.
20. When adjustment is correct, turn off both propane valves, stop engine and remove tool.
21. Install concealment plug, if equipped, then perform ``Curb Idle Speed, Adjust'' and ``Fast Idle Speed, Adjust'' procedure.