sounds like maybe the low-end needle is set a bit too rich? is it running differently in the plane than it was on the test bench? could be a difference in fuel tank location, so maybe you just need to re-tune it. maybe post or search in the Engines forum and see if you can get some help on that.
by the way, good luck on the maiden!!! Im building a 1/7 Jug for flight this spring, Im still in construction but should be ready to cover soon. Im looking forward to hearing about how she flies.
-ron