12391-ZV4-000 Honda GASKET, HEAD COVER (Honda Code 2794436).

Recommended Actions
Note: If the symptom only occurs under certain operating conditions (high idle, full load, or engine operating temperature), test the engine under the conditions. Troubleshooting the symptom under other conditions can give misleading results.Cold Cylinder
Use a 251-0030 Infrared Thermometer to check for a misfiring cylinder at the exhaust manifold.If there is an indication of a misfiring cylinder, check the following components for problems:
Spark plugs
Spark plug wires
Ignition transformers
Primary wiring for the ignitionInspect each of the spark plug wires for signs of pin holes and/or of electrical arcing.Refer to Troubleshooting, "Ignition Secondary - Test".Ignition System
Inspect the ignition transformers for the following conditions: loose connections, moisture, short circuits and open circuits. Inspect the primary wiring and the secondary electrical connections.Ensure that the correct transformers and spark plugs are installed on the engine. Inspect the spark plug wires for signs of pin holes and of electrical arcing. Check the spark plugs for fouling, correct gap adjustment, and moisture.Maintain the spark plug according to the Operation and Maintenance Manual.Incorrect Engine Timing
Verify that the base timing is correct. Refer to Testing and Adjusting, "Timing - Calibrate".Fuel Supply
Verify that the fuel pressure is correct. When possible, interview the operator in order to determine if fuel quality is in question. Try to determine if the source of the fuel has been changed.Ensure that fuel is supplied at a sufficient pressure that is stable. Check that the size of the fuel line is large enough to provide the correct volume of fuel. Inspect the fuel system for leaks.The following conditions can affect starting:
Low fuel pressure
High fuel pressure
Poor fuel qualityInspect the following fuel system components:
Fuel filter
Gas pressure regulator
Gas shutoff valve
Fuel actuatorVerify that the system components are operating correctly.Repair suspect components. Replace the fuel filter, if necessary.Incorrect Air/Fuel Ratio
Use a reliable exhaust analyzer to verify that the exhaust emissions are correct. Ensure that the carburetor is adjusted correctly. Refer to Testing and Adjusting, "Carburetor - Adjust" for the correct adjustment procedure.A change in the fuel energy content will change the air/fuel ratio. Obtain a fuel analysis.The fuel supply pressure must be adequate and stable.Strike the gas pressure regulator with a soft hammer. If the engine speed changes, inspect the internal parts of the gas pressure regulator for wear. Inspect the diaphragm for the gas pressure regulator for leaks. Ensure that the valve moves freely. The valve and the valve seat must be in good repair.Ensure that the fuel metering valve is operating correctly. Refer to Troubleshooting, "Fuel Actuator - Test" for details.Air Inlet Restriction
The maximum allowable air inlet restriction is 3.75 kPa (15 inches of H2O). If the air inlet restriction is higher than the specification, clean the filter element or install a new filter element. Check the restriction again. If the restriction remains too high, inspect the air inlet piping for obstructions.For more information, refer to Testing and Adjusting, "Air Inlet Restriction and Exhaust Restriction - Test".Exhaust Restriction
Measure the exhaust restriction during engine operation with a load. For data that is specific to your engine, refer to the engine performance data sheet.Investigate the cause of the exhaust restriction. Perform adjustments and/or repairs, as needed.For more information, refer to Testing and Adjusting, "Air Inlet Restriction and Exhaust Restriction - Test".Plugging of the Catalyst Substrate
If the catalyst substrate becomes plugged with debris, ash, or oil build-up, engine power will be adversely affected. High exhaust temperatures will result and the catalyst substrate may be damaged.Check the back-pressure of the exhaust system in order to determine if plugging as occurred. Refer to Testing and Adjusting, "Catalytic Converter Pressure - Test" for information that is related to measuring the back-pressure of the engine exhaust system.Throttle Actuator and Fuel Actuator
Check the movement of the valve for the throttle actuator. Remove the piping from the throttle actuator. Check that the valve is free of residue and dirt buildup. Ensure that the power is removed from the ECM. Check the valve for sticking by moving the butterfly valve by hand. The butterfly valve must move freely. Perform any necessary repairs.Check the movement of the valve for the fuel actuator. Remove the piping from the fuel actuator. Check that the valve is free of residue and dirt buildup. Use the override in Cat ET to move the actuator through the entire movement of the valve. The butterfly valve must move freely. Perform any necessary repairs.Incorrect Valve Lash
Check the valve lash. Refer to Testing and Adjusting, "Engine Valve Lash - Inspect/Adjust" for information that is related to adjusting the valve lash.Cylinder Head and Related Components
Measure the cylinder compression. Refer to the Operation and Maintenance Manual for information that is related to measuring the cylinder compression.Inspect the components of the valve train for good repair. Check for signs of damage and/or of wear to the valves and the cylinder head gasket. Inspect the condition of the camshafts. If a camshaft is replaced, new valve lifters must also be installed.