onan generator

Onan Micro quite 4000 generator ran perfect until I really needed it. I went to start it and it started and died. Sounded like it just ran out of fuel. When I hold the stop button to prime it, it makes a thumping noise that sounds like the fuel pump pumping but it also makes this clicking sound some of the time. Sometimes when I do that it tries to start but just fires a time or two. One time it did start and ran for 15 seconds or so and then died. I checked the codes and get a code three and then when I look at the second code it flashes a 36. Pushed button and cleared codes. The 36 comes back again. I've got 3/4 of a tank of fuel. Ideas?