340 Gets Terrible Gas Mileage

6 mpg?!
Wow! Are you sure?
Something is way out of whack!
Your timing doesn't sound too far off,
Id try a different carb.
what do the plugs look like?
is the gas tank leaking?...lol
Mine was when I bought it.

My 340 was getting 17 mpg with a Holley 670 sa.
Just switched to a 650 Brawler dp.
Mileage dropped to 16 mpg.
But it runs So much better!!
My car actually gets better Mileage in town
Then highway with a 904 and 3.73's
I hope you get it figured out.