I've had this happen when I had inadvertantly overflled the oil.
Going on the freeway the van would sputter and loose power, and then pass a huge gout of black smoke. About the time I was in the midst of pulling over and reaching for the fire extinguisher, it cleared up on its own, and I was on my way.  Sure startled the people behind me.

Don't know if the two are related, but that is the only time its happened.

Todd
'88 Westy

-------Original Message-------
From: Eric Zeno <vw4x4@FYI.NET>
Sent: 07/03/03 04:14 AM
To: vanagon@GERRY.VANAGON.COM
Subject: ON/OFF TEST Re: 1991 Vanagon sputters and blows black smoke on              highway.