I just switch over to Mobil Red Cap 15W/50 since it seems like so many Yamaha owners have had good results. I just drained my oil after 3 rides and it is really dark and smells sooty. I've always used Delo 400 15W/40 and changed the oil every 3 to 4 rides and never had the oil smell or look like that. Did this synthetic just clean out my motor? Any thoughts?