One thing I have noticed is, I suppose because they are so short-coupled, a biplane is more sensitive of horizontal stablilzer angle of attack.  Check to make sure your Hog is 0° or perhaps -1° (some negative helps avoid a "squatting" appearance in level flight).  If you applied full power from 1/3 throttle and couldn't gain altitude (only speed) it seems something was keeping the nose down. 

WWI bipes need about 1/2 throttle to land because of drag.  Do you have a lot of rigging on the Hog?