Onan Gen Set 5000 very rough start

Yes. The gas tank is completely full. . . I learned that one a few trips ago!! I found the governor arm and it moves freely. I did not find any other moving parts around the carb. The governor arm was attached to another moving part on the top left of the generator. . .approx. 8 to 10 inches away from the carb. It also moved freely with the governor arm. Could it be as simple as the spark plug?? How about the arrestor? When I hold the start button down it will really backfire. . .is this a carb. problem??

Again, thanks for the help so far and any other suggestions are certainly welcome. Please keep in mind that I am not completely lost mechanically, but almost lost!!