Testing in the air:

Today I flew my OS .40 fp on the fuel I mixed and static tested on 15 August. While the weather was cool and damp, starting and smooth running was as experienced while static testing. The power boost over my old high ether mix was apparent. Based on vertical performance, I'd say that I had at least a 10-15% increase in thrust (12 X 6 prop). This is a plain bearing engine that I purchased on eBay for $23.00. It is well-used; the pinch at TDC is long gone. I spent 25 to 30 minutes total time in the air with no difficulties at all. At the end of the day, I let it idle for 5 minutes or so while I picked up my gear. Then I went back and hit full throttle. It jumped up to peak rpm with only the slightest hesitation.

I pulled the head when I returned home. There was a very small amount of crud present, but it was very soft and soaked with oil--I could wipe it up with a rag. I suspect it collected while idling and looked likely to be blown out at normal flying speeds.

So here's my larger size engine vote for Stewart's brew using 11% 10w-40 diesel engine oil plus 11% modified olive oil for the lube.