Lil Wayne -- DROPPED By Mountain Dew ... Over Emmett Till Lyric

Lil Wayne will no longer "do" Mountain Dew ... the soda company announced it's DROPPING the rapper over a rap verse in which he compared the beating of Emmett Till to rough sex.

Wayne was a major spokesperson for Mountain Dew --starring in several commercials. Wayne began appearing in Dew ads in early 2012. Mountain Dew is owned by PepsiCo.

It's unclear when PepsiCo will stop running ads featuring the rapper.

Weezy came under fire back in February over a verse he dropped on the song "Karate Chop" ... in which he said, "Pop a lot of pain pills, 'bout to put rims on my skateboard wheels ... beat that p***y up like Emmett Till."

FYI -- Till was 14 back in 1955 when he was beaten beyond recognition, shot and dumped in a river ... after he was accused of flirting with a white woman in Mississippi. His open-casket funeral and murder trial were early flashpoints in the civil rights movement.