For all of you that provided suggestions, thank you. I found the problem and really feel stupid . I should have known better! The metal choke rod that I ran straight down and out the bottom of the cowling was resting against the Pitts style muffler. As soon as I removed the rod the problem went away and now both range checks (engine running/engine stopped) are the same . I fabricated a new choke linkage using nyrod and running it back into my canopy hatch area and out the side. It works perfect. Also, while running ground tests I found several other vibration induced problems (box holding throttle servo came loose from side of fuselage, one aileron with Robart hinges worked loose). Even though I balanced all rotating components there is still a lot of vibration with this big single. The engine runs beautifully and I know this baby is going to fly really well. Sure glad none of this has happened in the air.