Smoke from exhaust

Hello,
I have a 95 Cherokee and dark smoke is starting to come out of the exhaust, but only when I make a u-turn. The Jeep is running fine, except for the smoke and I noticed the problem about two weeks ago. While the Jeep is running there is absolutely no smoke, but as soon as I make a u-turn a cloud of smoke comes out the back that smells like burnt rubber. Does anyone have any ideas on what may be causing this?
Thank you for your time.

Have you had a peek under the hood? See if your valve covers are leaking oil. Oil could be backed up and spill into the cylinders when you turn.