This article is from the Chrysler-Plymouth-Dodge FAQ, by Dr. David Zatz with numerous contributions by others.
>After running for about 20 minutes the power drops out to the point
>where I have to pull over. If I am in "Park or Neutral" and step on the
>gas pedal, black smoke comes from the tail pipe.
With 2.6L engined minivans ... the airflow goes right
over the carburetor ... freezing it solid. Seconfd you stop, engine
heat thaws it out (which is why you can stop, restart, and it seems a
lot better). I put a metal shield in front of the carburetor
to deflect wind around it and it worked. Jonathan N. Deitch