The .46 FX with an 11-6 will be a little overpowered on a .40 size trainer. I would not expect it to ever die in the air, in a steep climb. A minor change in the tone is to be expected.

Are you flying it wide open? If so.... why? I could understand if you were flying at about 30% throttle, and the engine tone changed in a steep climb, but there should be no fear of engine stopping.

In my opinion, your trainer time is best spent flying around at about 30% throttle, except after you have progressed to the aerobatics practice stage. At that point, I see no need to fly at more than 30 % throttle except when preparing for a loop, or climbing into a stall turn, or other aerobatics.

At no time would I anticipate that a properly adjusted .46FX would slow down anywhere near quitting - especially not when throttling up and entering a loop or climbing into a stall turn.

If that's what you're doing, and the engine is slowing excessively, I suggest your high speed mixture needle is not adjusted properly - or there is a fuel feed problem.

Good luck,
Dave Olson