ive used all types of synthetic oils. big brands and no name...... i regularly pull my motor (custom ported 50cc a5) down for checks cause i rev the shit out it. synthetic dosent burn and it sticks to your internal components. almost like a clean sticky sludge, also sticks to the reed valves. this would causes friction and heat, plus it robs of top end power. the only fix is to run a lean mix, but thats never a good idea in a high performance donk, cause theres just not enough oil to go around for all your engine.
fuel does cool your engine but what happens when you pick shit in your carby with a lean oil mix..... and start leaning out...... theres your seize my friends..... take some time to learn about thermal barriers in a 2strokes combustion process, maybe it ill help you
ive also been running esso mineral oil but i mix it myself at 50:1 and im very pleased with its performance and lubrication.... thats good cause its real cheap......
never liked synthetic oil in air cooled 2 strokes and never will. a good tune with quality mineral oil mixed at 50:1 in my opinion is the best.
p.s stihl dont make synthetic oil, never have and never will. its just a ripper mineral oil. yes thats the blue oil and the red oil.. trust me im a gold level stihl technician. thier machines wont run right with synthetic. its been tested!
never used castor oil but ive heard good things about it....... dont even know if it mineral or synthetic. haha