Thats alot of junk built up on the 9 for only 1.5 hours......especially if you were on the pipe alot and you say it wasnt stuttering and seemed to run good.
On that setup, did it four stroke or foul at low RPM or idle ? What kind of fuel are you running. What kind of oil and what ratio ?
Second plug is looking fairly good, but, I woulda guessed you had a hour of run time by its looks.