From a physiological standpoint, the answer is straightforward. Olfaction, the process of smelling, is closely tied to emotion and associative learning. And, unlike our other senses, it’s wired directly into the limbic system; before you even identify a smell, the olfactory bulb has already triggered a memory and the feeling attached to it, a true primal reaction. So, if you grew up around motorcycles, your brain might associate two-stroke with the warmth of family, the pride of winning a race, or the satisfaction of tuning a carb. Getting a snoutful of the stuff can be comforting on a neural level.