I wouldn't be afraid to Hi tune the Ryobi engine, This engine is a tough little gem, inexpensive and easy to convert
I fly mine with a glow plug conversion (save on the electronic ignition) and run it with gasoline/glow fuel mixture see "gas fuel with glow plug no ignition" thread here on the engine conversion forum you will find a lot info. I am turning an APC 18x6W prop at 8100-8200 rpms with this mixture.