Fox Engines
In a recent Model Airplane News issue there was a .61 size engine comparison test. Dave Gierke, the tester varied the fuel and plugs to get the best performance from the engines. The Fox came out on top. He used 5% nitro fuel and a Thunderbolt plug for the best results. Go figure.
If you plan to run the Fox, you might want to get this issue and see how he ran it.