1999 Volvo Penta "WT" Models Workshop Manual, Page 39Get this manual
Engine Runs Rough If At Slow SpeedCheck:
Idle speed and idle mixture Engine timing and spark plugs Fuel pump pressure Water or contaminants in fuel Carburetor or manifold vacuum leak Internal carburetor fuel leak See ElectricalIgnitionFuel System Service Manual
If At High SpeedCheck:
Air leak on suction side of fuel system Too low octane fuel Ignition system secondary circuit Engine timing Wrong model or size carburetor, improper main jets or power valve, defective secondary fuel circuit, secondary vacuum diaphragm failure Exte'nal canister and carburetor fuel filters Fuel pump pressure Engine compression Water or contaminants in fuel, water in cylinders See General Information section and Electrical!lgnition! Fuel System Service Manual