The Stihl still has an intermittent miss-fire, mainly at high RPM. It can be heard in the flight video here:
https://www.youtube.com/watch?v=wwYrNwiMv2I
I have already reduced the spark gap to .5 mm, as with the recommended .6 mm gap, the engine suffered from high RPM spark breakdown and would not take full throttle at all. There are a number of possibilities I can and will explore when I get the time. I will bench mount the engine again and test until I get it sorted. I am not as rushed now that the plane has been inspected, registered and test flown.
Options include:
1. increase the spark gap up to .55 mm.
2. Decrease the spark gap down from the already .5 mm.
3. Change the plug to a hotter/cooler rated one.
4. Change the CH brand CDI --I have a cheaper Pegasus one from HobbyKing.
Beyond that, I don't know what to do. The battery power supply is 6.6 volt LiFe.
Any other suggestions most welcome.