General Motors — Carburetor Inspection and Cleaning
Testing & diagnosis
From a General Motors operator's manual covering: 181 CID, 3.0L L4, GMG-430, LW6. Check it applies to your exact model before use.
Applies to: General Motors 3.0L L4 (181 CID) engine
Before you start
- Do not attempt to measure gas pressure with a mercury manometer.
Procedure
- Measure gas inlet pressures at idle and full load with a water manometer. Do not use mercury manometer.
- If pressures correct, remove air valve cover and lift out spring and air-gas valve with diaphragm.
- Inspect diaphragm for holes or charring. Diaphragm should be reasonably flexible.
- Check inside diameter of air valve cup and fins on gas jet for grooves.
- Inspect inside diameter of gas jet and O.D. of small tapered gas valve for wear.
- Wash all parts thoroughly in kerosene or equivalent. For digester gas, wash in water and detergent.
- Reassemble cleaned or replaced parts, centering spring on air valve, and replace cover.
- From air-fuel outlet of mixer to throttle body, lift valve several times to assure free travel with spring closing valve.
- Check gas valve for leaks in closed position by sucking on gas inlet. It should be sealed.
- With engine running at idle, gas pressure should be 5 to 7 inches water column for 1050 BTU natural gas.
Tools required
- Water manometer Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Gas pressure at idle 5 to 7\" water column
- Full load intake manifold vacuum 2\" to 7\" mercury
- Gas pressure drop not more than 2\" water column
Source: General Motors operator's manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.