I've been sitting on this font ID question for several years now, clearly not trying very hard to solve it, but every once in a while it gnaws at me, so this is the day I post it. This is the logotype of a (now defunct) Spanish Motorcycle company which was quite successful in the late 60s and 70s. I'm sure that their particular logotype is a custom cut, in fact there are significant differences (typographically speaking) in the letterforms on the gas cap vs. the tank badge vs. the engine cases.

That said I have seen a font (or fonts) very similar to this on a bumper sticker or some Motorcycle mag ad from time to time and it always re-sparks the "what font is that?" question.