I am using OS Saito and YS fourstrokes. They all seem to be a set and forget when it comes to tuning. The OS is the oldest with the most run time on it. I quit counting past 25 gals. It has required the most valve adjustments,but only 2 times a year. That takes just a few minutes and it very easy to do. It is still one of the most realiable though. It has a very low idel and has never deadsticked. Some of the the guys I fly with us OS 120's and the really run great. Once you start using 4 strokes you will really like the smooth power and performance of them. I havn't had a 2 stroke since I sold my trainer, and do not miss it.