The propulsion system consists of - Fuel system, exhaust system, reduction drive, engine, and prop.Ultralight Aircraft Fuel system : Many ultralights come up for resale because the owner has medical, financial or family problems (or has simply lost interest.) The decision to sell usually does not come easily. This can mean that the aircraft has been used sparingly, and has been tied down, out in the open at a flying field, at the mercy of the elements, or hangared for long periods of time. If the reason for the sale of the ultralight aircraft is financial, aircraft maintenance should be of prime concern!In many cases the aircraft is left with fuel in the gas tank, and carburetor. Pull the cap off the gas tank, or the bowl of the carburetor you will know immediately whether the plane has been in storage. The smell will knock you off your feet! Adding fuel, or starting the engine without first draining and cleaning the complete fuel system, and replacing fuel line, fuel filter, vacuumn line, primer line can severely damage the engine, your body or the aircraft, when the engine quits from a clogged fuel system during takeoff! Consider the cost in time, and parts necessary to bring the fuel system back to 100%, when buying an ultralight.