I ran 20% nitro with 18% oil, never had a problem with mine.

Break it in slowly. Run the engine RICH! The only downside to a rich engine is loss of power. If you run it to lean from the get go, you will fry your piston and sleeve.

Here is a decent article describing the break in process. I would follow it if you are new to nitro RC.

http://rcvehicles.about.com/od/nitro.../f/breakin.htm