Hi:
I have a new ys .63. I ran it for the first time today, and ihad a problem with it backfiring. I richened the high end to about 3 1/2 turns out and that helped but it did backfire one more time. What will cause the engine to backfire, this is my first YS, and my first 4-stroke. I didn't change any settings out of the box except the high end mixture.I'm running the engine with an apc 12x8 on 30% heli coolpower.by the way it was about 40 degrees today.

Thanks
Stephen