Gas generator dies after put under load?

The gas generator is maybe 2 years old and recently has had a hard time running. It starts easily (a pull or two) and seems to run fine until load is added to it, than the load (lights, etc.) flicker as it goes rraaar raaar raaaarr raaar raar raar rar until it eventually dies. Maybe 30 seconds or so until it will die under load. Any ideas? Also the oil isnt that old and is already very dark, was thinking could be busted piston rings, but not sure.