I have recently done a motor swap on my camaro, i pulled out the lo3 and replaced it with a near 300hp 350, i also dtched all the computer stuff an am currently running an edelbrock 600 elec choke carb and hei distributor. My question is ever since i put the car on the road i have been getting awful mileage i mean 6-9 mpg at most 9, i have an a/f gauge and i know im running rich at idle but when i get on it the gauge goes all the way to lean but i know its not lean because there is no change in how the car is running. I want to get better mileage but i dont know where to start, im new to carbs so I could use all help and suggstions on what to do first, and also if anyone knows why my a/f gauge goes to lean when i get on it and back to normal as soon as I let off the gas that would be very helpful also. Thanks for all help ahead of time

 

First verify that you have the right jetting and rods in the
carb.
Do you have vacuum advance hooked up? (to ported vacuum)
is it working. (adding 10 to 20deg at high vacuum cruise)
what is your base timing? what does it advance to
(mechanical advance) should be 10 to 14 base @600rpm and
32 to 36 @ high rpm. Does it work smoothly ( advance weights/ springs. Rotor clearance)
Your car will idle at a AFR slightly richer than 14.7:1.
this allows for minor fuel distribution variences at idle
that all carbed cars experience. But should be no richer than
12.5:1 ... 13.5:1 would be better. If you can get it to idle at 14.7:1 more power to ya.
The car should cruise at between 14.0:1 and 15.5:1
It should go full rich when you floor the gas 12.5:1/ 13.00:1
A exhaust leak in front of the 02 sensor will draw in air into the
exhaust system giving you a false lean AFR reading.
Be sure to only adjust the idle mixture screws for best idle vacuum and smoothness after the car is fully warmed up.
Check for possible manifold vacuum leaks.

What manifold are you useing? What cam?