ORIGINAL: Kmot
I just opened my box for my Fuji .099 the other day. I bought it NIB from Hobby Shack in the 70's. Because of this thread I took a look at it again. It has a supplement in there, that has not been mentioned here. The supplement states to "read the instruction manual, do NOT run any fuel that is not castor oil based. Do not use synthetic oil fuels in this engine."
FWIW...
I have used fuel with 23% Baker AA castor and the engines were still a POS even after the 1 hour break in . My Enyas Still out power these and my version 3 from 1966 is still runnin' strong with lots of prop bounce. I do not run any of my bushing, iron piston engines with synthetic oil. I use total castor, that's why I still have all my original engines from the 1960's and 70's