diesel generator running issue

generally this to me sounds like slow fuel supply. The carb bowl fills up, you start it with a full carb bowl, it runs on that gas and whatever small amount gets also pumped into the bowl, but eventually the engine is starved for fuel as the bowl runs empty.
Mine has always been a carb issue, float related or something, but as others have said, a bad or slow fuel pump will give same symptoms. I bet it is nothing outside of either the carb or the fuel pump.