Thanks, I went back to my copy of Zen and the art of motorcycle maintenance and discovered that his pipes were turning blue when he left the mountains. Forgive me my transgression, it has been 25 years since I read it. Looks more interesting than I remember, I think I will read it again.
Incidentally, with my mind backwards, I was thinking of the problems aircraft have in developing lift in thin air. Obviously is different in carbs.