Fuel Delivery and Air Induction: Adjustments

1979-82 10-30 & 1500-3500 Series With Light Duty Emissions

NOTE: For curb idle speed specifications see; under hood label or Idle Specifications.

NOTE: Vehicles with a Gross Vehicle Weight Rating (GVWR) below 6000 lbs (8500 lbs for California), and passenger carrying vehicles with a capacity of 12 persons or less, are Light Duty Emissions Vehicles.

Fig. 61 - Propane Enrichment Tool Installation:

NOTE: Idle mixture adjustment requires artificial propane enrichment using tool-26911, or equivalent--Fig 61.

NOTE: Air cleaner must remain in place, and A/C control, if equipped, must be in OFF position--except where noted.

1. Disconnect and plug vacuum hoses as directed by Emission Control Information Label.
2. Connect tachometer to engine following manufacturer's instructions. Start engine and run at fast idle until it reaches normal operating temperature.
3. Place transmission in drive (manual transmission in neutral) and adjust curb idle speed to specifications:
a. On carburetors with a throttle stop solenoid, turn solenoid plunger screw.
b. On carburetors without a solenoid, and on models with an A/C speed-up solenoid, turn throttle stop screw on carburetor.
4. Disconnect crankcase ventilation (PCV) tube from air cleaner. insert hose with rubber stopper from propane valve into opening in air cleaner.

NOTE: Propane cylinder must be adequately filled and remain upright during adjustment to insure correct propane flow.

5. Slowly open propane metering valve while observing tachometer. Continue opening valve until engine rpm begins to drop and note maximum enriched rpm.

Fig. 62 - Propane Enrichment Specifications:

Fig. 63 - Propane Enrichment Specifications:

6. If enriched rpm is within specifications, Figs. 62 and 63, turn OFF propane flow and proceed to step 15.
7. If enriched rpm is not within specifications, turn OFF propane flow and remove plugs sealing mixture screws as outlined in Concealment Plug Removal.

NOTE: On models with limiter caps, remove limiter cap from each mixture screw, taking care not to damage screws.

8. Start engine and allow it to reach normal operating temperature.
9. Turn each mixture screw in (clockwise) until lightly seated, then back screws out equally, just enough so engine will run.
10. Place transmission in drive (manual transmission in neutral).
11. Turn mixture screws counter-clockwise equally, 1/8 of a turn at a time, until maximum idle rpm is obtained.

Fig. 62 - Propane Enrichment Specifications:

Fig. 63 - Propane Enrichment Specifications:

12. Adjust idle speed to specified enriched rpm, Figs. 62 and 63, following procedure in step 3.
13. Turn mixture screws clockwise equally, 1/8 of a turn at time, until specified curb idle speed is obtained.
14. Repeats step 5 then turn OFF propane flow. If enrich rpm is not within specifications, repeat step 10-14.
15. If equipped with a throttle stop solenoid:
a. Disconnect wiring harness connector to solenoid.
b. Adjust low idle speed to specifications with throttle stop screw.
c. Connect wire to solenoid.
16. If equipped with an A/C speed-up solenoid:
a. Disconnect wiring harness connector to A/C compressor and place A/C control in ON position.
b. Momentarily open throttle to allow solenoid plunger to extend, then adjust A/C idle speed to specifications with solenoid plunger screw.
c. Turn A/C OFF and connect wiring harness connector to compressor.
17. Remove enrichment tool an install PCV tube in air cleaner. Connect vacuum hoses to proper fittings.