I think the problem was the connecting rod. I have known of a couple of cases where the rod failed. Agape did fix the rod on one guy;s engine when it happened. The rod is bushed so you need to use a 20:1 fuel to oil ratio for break in and after it is run in really good, maybe 25:1 fuel to oil ratio. The other thing is that you need to use a really good quality synthetic oil, not the inexpensive stuff. I like to use Stihl HP Ultra oil in my engine. But Red Line or equivalent would work too. You need to use oil for air cooled engines. My 17cc NGH engine has been running really good for me, no problems actually with it in my case. I cannot tell you which version it is either, but it works. In my case I have it on a World Super Stunts .60 plane, but it doesn't need full throttle much though, as it can putt around slowly. The power output is quite good and I am very satisfied with the engine.