Evaporating Fuel in Carter 4-Barrel Carb?

Area to area and season to season gas composition will change. Gas will evaporate, agitation, heat, and other methods will accelerate the rate. Typically what is left behind when massive evaporation is induced is a low octane liquid (we got it to 78, Lab verified) and some chemicals. When you break down what makes gasoline you'll find there are components that "light off" fast/easier than others through the process. Gasoline composition these days are designed for evaporative emissions and exhaust emissions.

The issue with Ethanol is it draws moisture, absorbs more heat and it stoichiometry ratio is higher than gasoline, meaning you need to run a higher air to fuel ratio than gasoline to get the same pop. That's why you see flex fuel vehicles have worse economy on E85 than Gasoline. The second issue is all pump sell "up too X%" of Ethanol, meaning you might get 85, or 70.