No, my shutoff valve is not the cause. I removed the vacuum line from it today while it was idling and then repeated the above maneuvers with the same outcome...that would have been too easy!!
I do have a round compensator on top of the aft section of the IP that looks like the ALDA from my 1985 300D. It has the same adjusting and locknut setup on top of the round chamber. Do you think I should play with that?
Thanks for your time,
Brandon