Air/Fuel Mixture: Adjustments

Fig. 37 - Propane Enrichment Tool (Typical):

NOTE: Idle mixture adjustment requires artificial propane enrichment. A propane enrichment too, C-4464 or equivalent Fig. 37, is required to adjust idle mixture. Before proceeding, make sure that propane cylinder is adequately filled.

Air cleaner must remain in place and AC control must be in off position, unless otherwise noted, during adjustments. Disconnect and plug vacuum hose at EGR valve and 5/16 inch diameter control hose at vapor canister. Remove PCV valve from valve cover, leaving valve open to atmosphere. Connect jumper wire across cooling fan switch terminals so that fan runs during procedure. If equipped with fuel control computer, connect jumper wire between terminal on carburetor switch and ground.


1. Remove concealment plug and roll pin (1981) from mixture adjusting screw as outlined under, "Concealment Plug Removal".
2. Connect tachometer to engine following manufacturer's instructions. Start engine and run at fast idle until it reaches normal operating temperature.
3. Return engine to idle and place transmission in neutral. Adjust curb idle speed to specifications with idle speed screw on solenoid.

NOTE: It is important that ignition timing be within specifications during adjustments.

4. Disconnect air cleaner heated air door hose from 3-way connector and install hose from propane tool metering valve on fitting. Keep propane cylinder in upright position.
5. Open main propane valve fully, then slowly open propane metering valve until maximum idle RPM is obtained.

NOTE: Too much propane will cause engine speed to drop. "Fine tune" metering valve to obtain maximum idle RPM.

Fig. 39 - Propane Enrichment Adjustment Specifications:

6. With propane flowing, adjust idle speed to specified enriched RPM, Fig. 39, by turning speed screw on solenoid.
7. Turn off main propane valve and allow engine speed to stabilize.
8. Adjust idle mixture screw in small increments to obtain specified curb idle speed, allowing time between adjustments for engine speed to stabilize.
9. Open main propane valve fully, then "fine tune" propane metering valve to obtain maximum idle RPM.
10. If engine speed is more than 25 RPM different from specified enriched RPM, repeat steps 5-10.When adjustment is correct, turn off both propane valves.
11. On A/C equipped models, place A/C control in on position and momentarily open throttle to energize solenoid.
a. Remove idle speed adjusting screw and spring from top of solenoid.
b. Insert 1/5 inch allen wrench into solenoid and adjust A/C idle speed to specifications with A/C compressor operating.
c. Install idle speed screw and spring, then reset curb idle speed to specifications.
12. Stop engine. Remove propane tool and reconnect vacuum hoses to proper fittings. Insert PCV valve into valve cover and remove jumper wires from fan and carburetor switches.