Well if my bike sits for a while it blows white smoke out the exhaust. If it is steam, it sure "smells" like burned motor oil. On bikes I've had in the past, that blue/black smoke was accompanied by a gasoline smell. I guess replacing those little jets in the carbs with smaller ones must have made the rings or valves seal in some mysterious manner which I don't understand because the blue/black smoke disappeared....Dew.