My 340 getting 6 mpg

Dan Georgino said
Wooo, 750cfm is way to much carb. 600cfm is plenty. Then play with your jets till you get 18 to 20 vacuum inches at idle. What is your vacuum at idle now?

Yea im going to buy either the 600 or 680 Cfm Brawley vacuum secondary.

Vacuum was at 5 if i recall correctly