I don't know what the factory came with, but the aftermarket ones available are 5/16" that I've found.
Also, from my hydraulic system experience, the supply line to the pump is always bigger than the output pressure line. Not sure if that theory applies to auto fuel systems though.[/QUOTE
OK,
I concur wholeheartedly. Usually the pump's suction line is larger to reduce the line loss or restriction. On my RS23V0A GTX, the pump suction (inlet) is 3/8", After the pump to the vapor seperator is 5/16" and 5/15" thru th3 all the carb's fittings. There is a 1/4" line from the vapor seperator back to the tank. The vapor seperator has a 0.060" diameter restriction on the 1/4" connection.
Bob Renton