XRV650 Africa twin Stuttering and occasional black smoke

[Rolling Stone]

Need some help for a friend of mine in Namibia. Baz should be a new member by tomorrow.

the 650 has a slight stutter (Missing) when at speed and the occasional black smoke when accelerating at speed.
Apart from that the bike goes well.
What could be the problem?.

 

[Buzzlightyear]

 

[Rolling Stone]

 

[KTMRICK]

 

[KTMRICK]

 

[JJ]