A 1405 is an electric choke 600 cfm, correct? That should be fine and should not run rich. I ran a 1406 on my 318, 268h cam, headers, etc .... I hated the Flowmaster 10's, by the way. Way loud and I had a rap on decell, so I went to 3" with an H pipe and Flowmaster 40 series. My 600 Eddy was...