Glad to hear that things are working better. The YS engines do require some break-in as you've found. Once the settings stop changing, you'll know that the engine is fully broken in.
The nitro question was based on a lot of experience. There is a wide variety of nitro quality available and some guys are using cut nitro and don't even know. How much are you paying for nitro in Oz? It's still reasonably cheap in the US in 55 gallon drums.

Keep me posted on the progress with the engines. If you want to contact me directly use [email protected].

Good Flying,
Dave