Time for a New carb

You might try and find a nice 800 or 850 cfm TQ if you want better gas mileage with good performance. If you're not familiar working on them someone like Demonsizzler could set one up for your car.

I run an 850cfm TQ that I bought off Ebay on my mildly built 340-4psd and fine tuned it alittle more for my liking and it runs great.