Akon -- Justin Bieber Smokes Weed? I'll Talk to Him ...

Akon doesn't drink ... Akon doesn't smoke ... but Akon was pretty damn surprised when he found out his pal Justin Bieber might be doin' both.

Akon was leaving The Ivy yesterday when we asked him about the fan reaction to the photos of Bieber puffin' away on a joint, while surrounded by Coronas, at a recent hotel party.

"I gotta talk to Justin," Akon said ... "I didn't know he was smoking."

"That's my little man ... hopefully, I'll make an impact."

Akon's confident he can reach his 18-year-old friend ... telling us, "He's a responsible kid."