RE: K&B .65 Sportster (yup, more from me)
My Sportster .28 would not swing a prop larger than a 9x4 MAS until well after a gallon of fuel had been burned. Keep in mind that I wasn't using a fuel with much castor oil, which I attribute to the extended break-in period. It was S&W 10% nitro with mostly synthetic oil and a tad of castor oil. It did get to where it would spin that 9x4 at a pretty good rpm and it would stay running during the expected duration (as long as it had fuel). I tried running a 10x4 Graupner nylon prop, but the little .28 would overheat and quit. It was behaving just as though it wasn't broken-in. I did see another fellow running a prop larger than a 9x4 on a Sportster .28, but he was burning fuel with 22% castor oil, no synthetic oil.
The few K&B .65 Sportsters that I flew or saw flying (none belonged to me) back then were spinning 11x7 wood props (Zingers). They ran well on the 11x7, but refused to pull larger props with heavier loads unless the fuel was made with all castor oil lubrication. Those folks running 14x6 props must have had a lot of running time on their .65's or were burning fuel with all castor oil.
Ed Cregger