Regarding the diesel engine, they are sturdy little fellows. 90% of their problems when running rough or wont start are fuel system related. Diesel fuel if allowed to sit for long periods and if untreated can be a breeding grounds for bacteria which in turn can clog your filters and build up sediment at the bottom of the tank. You should have a filter/water separator which is called the primary filter and then an engine mounted filter known as the secondary filter. When you replace filters you may need to bleed air from the fuel lines (Google procedures). Some engines are raw water cooled and others have a heat exchanger and use automotive type coolant. The difference is the liquid that flows inside the engine passages but both draw and exhaust raw water for cooling. That means periodically replacing the impeller and keeping the mixing elbow clean. The oil in a diesel usually turns instantly to black but that is normal, it is hard to suck out all the old oil and slightly worn engines have combustion by-products contamination. Dirty oil is not a problem that is why the oil filters are there for. Heat is worst enemy of oil as it degrades the viscosity. By the way do not use anything thinner than 20W40. The pull cable to shut the engine off activates a fuel cut off valve. At the control panel you will likely have a Tachometer, a key switch (diesels do not have ignition) a starter push button and warning lamps and a buzzer for 1) low oil pressure, 2) overheating and 3) not charging. There will also be a toggle switch to test the overheating lamp and the shutoff cable. It is normal to have some slight engine vibration at different RPM points but if excessive suspect the motor mounts which can look good and be shot but also check engine alignment and propeller shaft. Yanmar has a strict dealers agreement which means only the authorized dealer in your area can sell you parts. Go their web site and find out who the dealer in your area is. Pricing is controlled and availability is quite acceptable. Try to get a shop manual for your model engine if you plan on doing your own repairs. When the engine smokes it is ndicative of its condition; White smoke is water vapor or overheating, bluish smoke is burning oil, black smoke is overfueling and can point to a clogged mixing elbow or fouled propeller. The engines do not like to idle at low RPM so keep them around 900. Diesels operate at high compression and can get quite hot so before shutting the engine off let it idle and cool off for about 5 minutes. Hope these short list of hints can be helpful.
