There's probably no topic sure to ignite a controversy of opinion than oil content and type. You'll hear lots of folks declare they used XYZ fuel and had no problems. The fuel manufacturers will all swear their blend gives the "most power", "cleanest burning" and "longest life" of any fuel.

On the other hand, I know a lot of engine rebuilders who know exactly how quickly any engine can be ruined by running a fuel with insufficient oil or no castor. Ask me how many engines I've bought used which are worthless because someone ran it with "RC Fuel".

I have several OS FP and LA plain bearing engines. All are ABN (aluminum piston, brass cylinder which is nickle plated). Manufacturers used to use ABC (chrome plated) but most went to nickel due to environmental concerns, costs and quicker break-in. For breaking in, I use Sig Champion fuel which has 20% oil which is 50/50 synthetic/castor. Castor provides many benefits and one disadvantage. It cools better, protects better but will eventually cause a varnish buildup. There is no better lubricant for model engines than a high grade of castor. My cast iron/steel Fox 35 Stunt control line engines have to use at least 27% castor fuel.

My engines are broken in using a fuel containing at least some castor and NEVER less than 18%. If in doubt, add a few ounces extra castor - more is better than less.

Use a small prop and don't lean it out more than a 10 second burst.