Light Duty

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.

NOTE: Idle mixture needles have been preset at the factory and sealed. Idle mixture should be adjusted only in the case of major carburetor overhaul, throttle body replacement or high emissions as determined by official inspections. Adjusting mixture by other than the following method may violate Federal and or California or other state or Provincial laws. Because of the sealed idle mixture needles, the idle mixture checking procedure requires artificial enrichment by adding propane.

1. Set parking brake and block drive wheel. Engine must be at normal operating temperature and air conditioning off.
2. Disconnect and plug EGR and cannister purge vacuum hoses.
3. Connect an accurate tachometer to engine.
4. Disconnect vacuum advance and set timing to specification. Reconnect vacuum hose. Ignition Timing
5. Set carburetor idle speed to specification. Adjustments
6. Disconnect crankcase ventilation tube from air cleaner.

Fig. 61 - Propane Enrichment Tool Installation:

7. Using tool J-26911, insert hose with rubber stopper, from propane valve into crankcase ventilation tube opening in air cleaner. Propane cartridge must be vertical.
8. With engine idling in drive (neutral for manual shifts) slowly open propane control valve while pressing button. Continue to add propane until speed drops due to over richness. Note maximum engine speed (enriched speed).
9. If the enriched idle speed is within the enriched idle specification the mixture is correct. Go to step 17.

Enrichment Specification: Specifications



10. If the enriched idle speed is not within specification, remove mixture screw plugs as follows:
- Remove carburetor from engine to gain access to the plugs covering the idle mixture needles.
- Invert carburetor on a suitable holding fixture, manifold side up.

NOTE: Use care to avoid damaging linkage, tubes, and parts protruding from the air horn.

- Make two parallel cuts in the throttle body on either side of the locator points beneath the idle mixture needle plug (manifold side) with a hack saw. The cuts should not extend more than 1/8 inch beyond the locator points. The distance between the saw marks depends on the size of the punch to be used.
- Place a flat punch at a point near the ends of the saw marks in the throttle body. Holding the punch at a 45 degree angle, drive it into the throttle body until the casing breaks away, exposing the steel plug.
- Holding a center punch vertical, drive it into the steel plug.
- Then holding the punch at a 45 degree angle, drive the plug out of the casting.

NOTE: Hardened plug may break rather than remain intact. It is not necessary to remove the plug completely, instead, remove loose pieces.

- Repeat procedure for the remaining mixture needle and re-install carburetor.
11. Using tool J29030 or equivalent, lightly seat mixture needles, then back out equally, just enough so engine will run.
12. Place transmission in drive (automatic) or neutral (manual).
13. Back each screw out (richen 1/8 turn at a time until maximum idle speed is obtained). Then using base idle speed adjustment screw, set idle speed to the enriched idle specification. Specifications
14. Turn each mixture screw in (clockwise) 1/8 turn at a time until idle speed reaches base idle speed.
15. Re-check enriched speed with propane. If not within specification, repeat adjustment beginning with step 12.
16. After adjustments are complete, seal the idle mixture needle setting using silicone sealant or equivalent. The sealer is required to prevent tampering with the setting and to prevent the possibility of loss of fuel vapors.
17. Check and adjust fast idle speed. Adjustments
18. Turn off engine. Remove propane tool, connect crankcase ventilation tube. Unplug and reconnect vacuum hoses. Install air cleaner.