Joy,

Black exhaust when warm:

The first thing I would check is the ground wire that is located on top of
the left side of the engine.

The ground wire in question is the brown wire that is included in the wire
sheath that holds the wires that go to the Hall sender.

If you have air conditioning, this ground connection is just below the a/c
compressor.

If your Vanagon is a syncro, this ground may be attached to one of the oil
breather mounting bolts.

Michael

My VW web page:
http://www.velocity.net/~vickrail/moshevw.htm