Thanx guys. This has described my situation very well. I have a Plus 21-5 and Plus 21-5K both treated the same way. Both have between 4-5 gallons and now the carbs are "balanced" better, they are not performing like they should. So I'm sure new pistons and sleeves are in order. I have never really had "lean bog" on high end or low end. The engines just never performed like I had expected. Both engines were good, but that's all I could say. Once I got the carb balanced as described here both engines seemed to come to life. But now the engines are flaming out and the tune seems to wander a bit. So fresh bearings and new P/S/R sets should set them on kill, especially after breaking in correctly and have the tune closer to what it should be.