Both my .46 and .55 AX's have been excellent. They started easily and idled perfect right out of the box. The only adjustment either has needed was a little leaning out of the low-end once they'd ran a while. Neither has ever quit in the air. I see a lot of guys at the field fighting with low-cost 2-strokes; I think that the AX series is well worth the extra cost compared to other engines. I was going to put a 4-stroke in my Twist .60 but I may end up ordering the new .75-AX.