[Karl Bebout]

Hauss, way back in the day of only leaded gasoline (Amaco high test excepted), any car, in tune, would have light gray exhaust pipes, after several miles at highway speeds. No plug issues, always thought the color came from the lead in the fuel. I'm not a chemical engineer, just a geezer with lotsa miles on my clock.
Varmit, I don't understand how the molecular density of the fuel would make any difference in the float setting. Idle mixture and/or jetting, yes, but wouldn't affect the buoyancy of the "bobber", would it?