Hi,
I run the same engine in a large Giles 202. Runs superb and starts first back flip every time.
10% sounds way to much for this motor as they are european they tend not to need much, if any nitro at all. I actually run mine on half a gallon of castor straight mixed with half a gallon of 5% sythetic givig an easy 9k on a 16 x 8 APC.
Great engine. Try reducing the nitro content and add some castor if you're not already using it.

Regards,
Tony