Unlike gasoline engines, diesel engines will not draw fuel from the fuel tank if the fuel lines and pumps have gone dry. An engine that has not been run for a week or more may have had the fuel bleed from the lines. A diesel that has lost its prime will not start until fuel is back in the lines and pump. Diesels will have a priming pump or bulb located somewhere on the fuel system.
Cold weather has two effects that makes diesels difficult to start. Cold fuel vaporizes poorly making ignition difficult and cold engines tend to crank over slowly reducing compression build up in the cylinders. Diesel engines will have glow plugs or pre-heaters to warm the air and/or cylinders. If starting is difficult in cold weather, ensure these heaters are functioning properly. A decompression lever will allow a cold engine to crank to a faster speed before applying compression, assisting the start process.
Diesels function solely on properly vaporized fuel and compression. Black smoke after an engine has started is an indication of poorly vaporized fuel. Blue smoke is an indication of oil in the compression chamber, which means the engine is losing compression due to bad rings or a scored cylinder wall. Compression problems will require a rebuild or replacement of the diesel engine powering the generator.
Improper fuel vaporization is a major cause of diesel starting problems. A fuel additive with detergents is the first step to remedy injector problems. If the additive does not make starts easier, the injection system should be checked out and repaired or replaced.
You can purchase engine starting fluid at auto parts stores and truck dealerships. This spray aerosol of ether and petroleum products will help start a troublesome diesel generator. Remove the air cleaner cover and spray a two-second burst of starting fluid into the air intake while cranking the engine. If there are no other problems with the engine, it should start immediately. If the engine does not start, it has deeper problems and repeated use of the fluid will not help.