Warbird Information Exchange

While running the engine, after warming it up, when advancing the throttle the MP went down and stayed there almost fixed. It would not change with a change in the throttle position. I disconnected the MP line, blew it, checked the connections and found all good. I also looked at the intake tubes, carb, exhaust and found nothing unusual. Changed the gage - no change. Any ideas?
Jake

Did it always do this? Are you sure it is hooked up to the right place on the engine?