ys engines are harder to tune but it's easy to get the hang of it. when you have your engine tuned right, it will be more reliable in every way than the competition and have more power too. ys engines are competition four strokes meaning they are made to compete with other two strokes of the same class. ys engines will also have a better throttle transition and a better inverted idle because the low end affects the idle mixture ONLY instead of everything at once until full throttle. the low end controls the idle mixture so you just lean it out until it won't load no matter which way the engine is mounted, the regulator screw affects the midrange more than the other adjustments (becasue the low end is idle only and the high end is full throttle only) but you will have to compensate a bit for the increased-decreased flow with the high and low end. trust me. get the 63 and you will not be dissapointed. i used to be an os supporter but i will never leave ys for four strokes. i have really found the best.