I have 3 Saitos (82, 100, 125) and a recently acquired FS-OS91 II. The Saitos are great but I really love the OS because of its rock solid idle. After I broke in the OS, it's idle was very rough. I did a valve adjustment and it smoothed it right out. OS sells a valve adjustment kit for around $10.00. My OS keeps getting stronger the more I fly it and is currently my favorite engine.