Jim is a lot smarter than I am, but;
Larry Foster suggests that one use 25% castor and 3% klotz in his new Fox engines along with 15% nitro. I use this in southern California and it makes all of my old Foxes, K&B's and McCoys sing. They are all old and well run, gummy and all with old castor, except one L&J Fox 35 and one T&L McCoy 40. I thought I might lose some compression on the older jobs with the 3% klotz but it didn't come to pass.

I would try to add enough oil to bring the total oil content to 28% and run them at a nice four cycle and see how they run.

Chris...