The air/fuel mixture is measured by sampling the exhaust with a CO meter. If this equipment is not available, no checking or adjustment is possible. Since adjusting the mixture is not part of a normal tune-up, the adjusting screw is protected with a tamper-proof plug. If the air/fuel ratio is obviously incorrect (lean miss, sooty spark plugs and tailpipe), or if the CO measurement is out of specification, look for other problems such as a vacuum leak, bad sensors, loose electrical connections, and correct any faults before deciding to adjusting the mixture.
- With the engine at normal operating temperature, make sure the ignition timing and idle speed are correct. Stop the engine.
- Unplug the blue coolant temperature sensor connector.
- Raise the dipstick slightly to allow for crankcase ventilation. Clamp the crankcase breather hose near its control valve.
Start the engine and measure the CO content; it must read 0.3-1.1 percent. If adjustment is necessary, remove the mixture adjusting screw plug as follows:
- Center-punch the mixture adjusting screw plug.
- Drill a 3 / 32 in. (2.5mm) hole approximately 5 / 32 in. (4mm) deep in the center of the plug. It is helpful to apply a small amount of grease to the drill bit to catch the metal shavings.
- Thread a 1 / 8 in. (3mm) sheet metal screw into the hole.
- Remove the plug using a pair of pliers.
- Insert a 5mm Allen wrench in the hole. Adjust the CO to the proper level following the graph.
- When adjustment is completed, carefully drive a new plug into the adjusting hole.