MEP-803A?

I have an 804B and I am pretty happy with it. I have put 400 hrs on it, it had 2 hrs when I bought it. They are very reliable in general but do need maintenance, especially if they have been sitting for a while. I did have to replace the fan belt, batteries and voltage regulator. I would say you definitely want to see it running and with minimal exhaust smoke once it has warmed up and minimal crankcase pressure out the oil dipstick. Good luck!

Very broad question. This is a constant speed application and is very different from any kind of vehicle diesel application. These are great units. Diesel fuel and variants are acceptable. But stick to diesel. Do not use Kerosene ever.