As already pointed out twice above, the song played over the MEDIUM COOL opening credits / motorcycle scene (and at various other points in the film), is indeed the instrumental "Emotions" from the 1966 self titled debut album of the Los Angeles group LOVE. Cool little song.

The song is called "Emotions" by the band Love.

I believe that song is "Emotions" By Arthur Lee's Love. I think you can find it on their eponymous album. See the following link:
www.cduniverse.com/productinfo.asp?pid=2342037&cart=191479873&style=music
Unfortunately you can't sample the music for that album to check.