Find out which point on the mixture curve is closest to where the stick is when it bangs and then richen that point a percent or 2 at a time and do the same for the point before and after it and see what happens. Make sure your transition is still good. I think you may also get a better idle with a higher nitro fuel. Most everyone I know running these motors in the states is using 15% nitro with anywhere frome 16-18% oil. Like I said before, the cooling of the main bearing and pump area are important too.