I have two engines that I am going to be breaking in. A OS 91 FX and a BGX 3500.

The question I have is which fuel should I use ?

I have Byrons fuel 15% nitro and 20% oil. I like the 20% oil for breaking in purposes, but not the 15% nitro. Would this be too much nitro for breaking in purposes ?

I also could use 10% nitro and 16% oil as an alternative. Should I up the oil % by adding Klotz castor oil to 20% ?

Thanks in advance. Cary