Honda GX 160 under 30 hrs from new, is running poorly

Honda GX 160 under 30 hrs from new, is running very poorly, and subsequently not generatinfg electricity; have tried new BPR6 ES spark plug but without change in condition; recently changed engine oil with Honda lube (10W30, surely unrelated?). Suspect fuel? Air filter clean enough, blowing some black smoke out of exhaust when turning over prior to starting before running approx half speed, vibrating a bit and then sputtering and finally stopping. Will now try the fuel sediment cup, but I always have used freshly bought fuel prior to filling/starting generator.

My model does not seem to have a hand throttle lever fitted, only a choke lever, I'm guessing a generator (Pramac 3000 in this case) should not require any modification of running speed once set by the maker? Any suggestions gratefully received, thank you.