Generac Generator, no power after running a few minutes

You may want to consider that the thermal switch controlling the dc to the rotor is bad or the rotor is drawing more amperage than it should.
Oblong, dark brown Bakelite frame, two spade connectors, small adjustment screw. Located inside the panel board.

Also, the stator has a one time thermal fuse imbedded in the winding. If it blows, use the other wire coming out of the stator that bypasses the thermal fuse.

JimL