Another AA Senior/Fox 35 question

For the brief time the AAS flew Sunday afternoon, I learned something about Fox 35s that I had not experienced before. being short on fuel, and wishing to see the effects of higher nitro and a little synthetic oil, I mixed some 20% nitro w/50-50 22% oil with some 10% N-29% castor. About a 50-50 mix. Engine ran fine, but broke HARD in manuevers. Also couldn't make it to the sq. rectangle at the end on the seond flight.
I think I needed some head shims.
The AAS should fly at Huintersville!
Bill <><