I have a 78 F150 with a 300 engine and the Carter YF 1 barrel carb. I have a sputtering/popping when I am not giving it any gas and going down hills. As I remember from an old Comet, I think this is the air/fuel mix adjustment on the carb. Can anyone tell me if Im right and do I need to back out on the screw or in? Thanks!

 

The Air/fuel mixture adjustment is only for the Idle circuit.

Your problem is more with other carb circuits.

Check the fuel filter & accelerator pump .

My thought is a leaking butterfly rod allowing air to be sucked in through it.

Spray some carb cleaner at the rod where it sticks out the body of the carb (not in the top where air is supposed to go) & see if the engine changes how it runs.