BJ, as the intake charge moves toward the intake valve and into the cylinder it has momentum, when the intake valve closes this causes the intake charge to stop suddenly and it compresses slightly then bounces back toward the carb spraying fuel all over the inside of the cowl and firewall. The velocity stack reduces this considerably and increases fuel economy. The little 30 and the FA .40a have the velocity stack cast as part of the carb body.
Last edited by Hobbsy; 02-23-2015 at 07:50 AM.