I Have a OS 61fs that is 10 yrs old and i first put it on the plane and fly it , I think it has lasted so long becuse i allways run it just alittle rich it leaves a little more mess but windex is cheaper than a new moter , there is a man in my club that runs a tank of fuel a new motor then it's balls to the wall and he goes thru alot of motors and i'm still flying with my 10 yo OS and i have many more OS motors that fly fine out of the box , so my advice is allways run just a little rich till you learn more about motors and do like i do and let someone else burn up there motors and learn from there mistakes