cam question

I'm getting slightly less mileage with my set up. About 1 - 2 mpg's.
I have a Holley ready to bolt on for chits and giggles and comprao at the track.
It's a 4160 convetered to a 4150, E choke and vacuum secondary.
Stock engine just taken aprts to have a look. It's gettin tired, but not to bad.
Rebuild soon.