Suburban 3/4 Ton 4WD V8-305 5.0L (1986)
Air/Fuel Mixture: Adjustments
Federal
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. See: Ignition Timing
5. Set carburetor idle speed to specification. See: Fuel Delivery and Air Induction/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: See: Idle Speed/Specifications
