Yeah hate to break it to you but nitro needs constant tuning.  I would try turning in your HSN 1/8 of a turn and see what the performance is like.  If it's good, try another 1/8 of a turn.  You need to experiment with it to find the sweet spot.  You can keep going lean until it loses power (be careful to not run it lean too long) and then back it off a bit. Patience, tune, patience, tune.