J/30 Class Association Forums J/30 Forum The Boat, Sails and Equipment Engine Problems

Made it out of the Annapolis Harbor yesterday when the engine started shooting out white exhaust smoke, engine knocking very loud and then stopped. Got back into slip and checked everything; looked OK. Engine started and within 30 seconds it began again. Any ideas out there? Any thougths on what an overhaul will cost a Yanmar GM20?