It means the activity of putting one's face between a woman's breasts, and rocking turning one's head rapidly from side to side while making a noise like a motorboat.
"Put your head between her tits and go bbl bbl bbl bbl bbl..."

Taken in the contest of the song Baby's Got Back by Sir-Mix-Alot he is referring to Florence Griffith Joyner a track athlete in the 1988 Olympics who defiantly fits all the other descriptions of what he likes in women mentioned in that song. Not some soda why on earth would you want to keep your women like a soda anyway?

The placement of one's face, specifically the mouth, into the area between a well-endowed woman's breasts, followed by a rapid shaking of the face in a side-to-side motion accompanied by yelling. The resulting sound that is created sounds similar to an outboard boat motor.

Sticking your face between a ladys fun bags and blowing hard allowing the boobies to wobble on your cheeks.

The act of making an engine noise when sticking your face in a woman's BOOBS.

A great way to end an awkward conversation with a girl you don't want to talk to.

The act of making a monotone hum while pinching and moving the cheeks back and forth