Brodak CL Basic Trainer 049

If I'm reading your post correctly, your saying that your oil content is 30%. That to me is too much oil and while the engine will run, it's going to be down on power. Cooler weather will also cause a dramatic impact on full castor fuels.  A Cox engine is completely safe and happy on 20% oil. Sig Champion fuel is 50/50 castor/synthetic with a total of 20%.  This is from the Sig site so there's no confusion 25% Nitromethane
20% Lubricating Oils
(1/2 Castor, 1/2 Klotz)

Running full castor also preferred by some but your going to need to remove varnish on frequent intervals especially in hotter weather. Letting the engine sit unused for a few months will cause the engine to lock up using all castor. I've used Sig for years without any issue. Sig has been my fuel for years but over the past couple of years Sig has been struggling. Sig has had numerous owners and orders have been more than problematic. I've had to mix my own up until recently. I prefer more synthetic than most and never had issues doing so as long as my oil content has been no lower than 20%.