Not that it's overly relevant to the topic at hand at what I assume powertrain use, but within British car communities among people who prefer a thicker carburetor oil, as to whether 20W-50 engine oil, xW-90 gear oil, or SAE 30 is most appropriate. Carbs tend to run relatively cool thanks to the vacuum/fuel atomization, and I've measured 120-130ÂºF when properly warm but not heat-soaked with an IR thermometer. I know there's some variance, but at those temperatures they all look pretty similar to me. Since the only purpose of this oil is to slow the rise of this piston(it doesn't really lubricate anything) friction additives and detergents don't matter. Dampening the piston movement replaces the accelerator pump in this type of carb, which can otherwise feel a bit less responsive than a fixed venturi carb w/a pump, and the idea behind thicker oil is that it will enhance this effect. I've actually gone as high as SAE 50, although it's hard enough to find and another oil to keep on hand that I quit bothering and went back to either engine oil or gear oil(gear oil often wins just because the nozzle makes it easier to not make a mess).