Well Minn, I have a YS 1.20NC that will kick your mule if you try to tune it by ear. You just can't hear a change?? Not only can't you hear the change but the high end needle can be twisted a lot before you hear the drop. Why is this?? I don't have a clue. It's the only engine I have that is like that. Same thing with the low end but the old NCs used the pressure screw to adjust the low end, no low end needle on this one. All my other four strokes are easy to get the tune by ear or at least close. I still use my tach a lot when setting up a new engine and testing props. BACK to the question. About the only reason for using a four stroke is the noise and they have a smoother power band through all the RPM range and swing a bigger prop because of the torque. To maintain mine I just check the valves once a year and adjust if needed. All but one of my four strokes is a pumper of one type or another. With a pumper you can get away with installing your fuel tank any place you want in the plane. There are a lot of other little reasons for a four stroke but for the most part it's the cool factor.