If you are using a 18x6 what kind of rpms are you acheving? I usually get around 9000 to 9200 richened for flight on the APC 18x6W. My plane is 12.25 pounds and hovers around half throttle. Pull out is not a rocket using a 6 pitch but it is steady and positive plenty for good 3D. I find I have to usually pay good attention to the throttle because it will easily start climbing in a torque roll even at half throttle.