[Jim Caughlin]

Originally Posted by JGrossijr

One purpose for covering the cup is to contain the light ends that evaporate from the fuel when exposed to atmosphere. [https://grassrootsmotorsports.com/ar...oline-it-ages/

Put a cup of race fuel in the sun and see how long it takes to totally evaporate. Ever notice when you spill race fuel on the ground, it's gone about as quick as it hits the ground.