FWIW ----This quote:
"Marvel Mystery oil is a very light naptha-based machine oil with
wintergreen and a little phosphorous in it.
Many lightplane owners use it as a gasoline additive. It burns pretty clean
 in small quantities and isn't as gimmicky as it sounds. "
is from, this link:
http://vger.rutgers.edu/~ravi/bike/pages/pages/docs/storage.html

Doug
'84 Westy
Toronto, Canada