Most trainers don't do outside loops very well. Set up as in the instructions, most will barely hold inverted level flight, never mind turn or pull up while inverted.

But you can get better outside looping by increasing the down elevator travel and moving the CG back. Going to a prop with more diameter and less pitch can also help the inverted flight, I'm using an 11x5 APC on an LT-40 with an Evolution .45 trainer engine. It's a pretty good combination. Oh, and I took the baffle out of the muffler for a little extra power.