I would contact the company (Hobbico) about all of this... see what they say.

I have an OS FXi engine in mine, and another plane (my slowpoke) with an OS LA engine, and the FXi engine runs MUCH better (although after well over 100 flights in three months, I've only had ONE deadstick, this week, due to lack of fuel)...

I'm shocked you're having trouble with the FX engine.