I had a similar symptom on a 79 Olds Cutlass years ago.  It turned out to be 
blockage in the exhaust system caused by the catalytic convertor freezing up 
after running a few miles in freezing temps.  When we disconnected the exhaust 
from the engine it ran fine. Since I could legally drive this way I had to 
replace the convertor.  Hope this helps in your diagnosis.

Karl 88GL

	cbennett @ kpmg.com 
01/06/97 10:28 AM
To: vanagon @ lenti.med.umn.edu (Multiple recipients of list) @ Internet
cc:  (bcc: Karl G Vochatzer/AMR)
Subject: Rough running when Hot

Hi there,

I have a probem with my 86 Vanagon GL.  It starts right  up, even on the coldest
mornings, but when it has warmed up, it starts to misfire, running too rich,
black smoke out the exhaust, and with  no power to pull even the smallest hill. 
But when I turn the motor off and start it up again, it runs fine for awhile,
and then the misfiring starts again with the black exhaust smoke.

The vehicle had been setting for about a year, and I thought it might be bad
gasoline, but after several tanks, it still has the problem.

Any ideas as to what would cause these effects?

Charles