Calibrating the right air/fuel mixture is important to gain proper power and efficiency from your carburetor and engine. But for vehicles running E85 fuel, proper calibration is difficult if you don't know the exact percentage of ethanol to gasoline in the fuel. These Holley E85 fuel testers are essential tools that can instantly determine the ratio in the E85 fuel you're using. They fit in your pocket or toolbox and are easy to use. Simply add water to the first line on the testers and then pour in the E85 sample to the second line. Once the water is absorbed, the Holley E85 fuel testers will indicate the amount of ethanol in the fuel.