Best way to find out if the lines are 3/8" or 5/16" on a 67 cutlass Supreme convertible without pulling the tank ahead of time. ?

 

Measure the OD of the line.

 

To clarify, measure the OD of the metal hard line. The diameter is the same from the tank to the carb, so unless someone has mucked with the factory lines, you only need to measure the line at the carb inlet. My money is on 3/8" for a 1967.

 

appreciate it. If

 

iirc, 5/16 for 330 engines, 3/8" with 1/4" return line on 4-4-2.