Fuel solenoid valve faulty. Replace fuel valve if it does not open when power is applied. Low generator voltage output. Adjust generator RPM for proper voltage under full load conditions. Burner will not fire, plus diesel fumes are emitted from the exhaust port.
Unburned fuel can saturate it and cause a fire.
Fuel to air ratio out of adjustment. Set air band and fuel pressure to specs. Fuel nozzle partially clogged. Replace nozzle of proper size. Ignition transformer not providing spark to fuel.