My son was standing behind my 919 one night while it was running and he had black specks on his face afterwards. The bike had been ridden pretty much every day before so it definitely hadn't been sitting.
Admitedly the bike had been sitting for a while. But its always hot as hell in these parts, condensation unlikely. Will repeat the exercise and take better note of what I'm seeing.
Does the "running rich" reputation of the 919 cause unused fuel to splatter?
It's just a temp change, unless ur rings went south from sitting so long j/k no really Oregon weather does this all the time, sometimes it gets really bad, cars, trucks and bikes, there's been times when I fire up my DRZ even in the summer and it will start blowin water/fuel/black crap out the exhaust, sometimes daily it's a pain to keep it clean in the winter
In the end, if it's not a lingering smoke or steam(antifreeze) then ur all good, just keep it away from the walls and white cars :-)