Mark
checking manifld vacuum would be a good idea and setting the CO with an exhaust gas analyzer would be a big help have you checked the compression also what have you done to the engine before this problem started. its a hydraulic lifter engine and the lifters are known not to let the valves close when the engine is hot see the hydraulic lifter article on my web site 
http://www.bostonengine.com 
Bob Donalds  

mark wrote 
A question for all of you who know a bit more about the type IV motor than
I. our 82 Westy starts and idles, but not that well.  At idle it surges on
about a 1 to 2 second schedule, meaning it idles at about 850-900 for 1 to 2
seconds and then  is slowed for about 1/2 second.  Also, it is generally
down on power when driving, almost the same as when it was only running on
three cylinders, but all four have gas and spark.  This is not a miss, nor
does it appear to be a vacuum leak that I can find.  Any ideas?

Mark
82 Westy