My 340 getting 6 mpg

trapster said
I think I am getting about 8 in my 64 dart with 340 3.55 gears 10.5 to 1 CR 750 vac sec 284 484 cam

one thing to consider is everytime you stop the gas in the Carb evaporates pretty quickly.

Only if there's something wrong with your carburetor or you have a major heat soak issue.

I've never had that issue with my Holley double pumper, even in 110° temperatures. Even the Edelbrock I run on my truck takes several days.