Rich or Lean? or in between?

[66StangGuy]

my next project.

carb.

trying to figure it all out.

is my motor running rich or lean?

installed new plugs. old ones looked new not very old.
ran the motor for a week or so driving around normally.
checked the plugs and they look like brand new. very clean.
put my car on the smog machine at work and a\f ratio was 25:1
reved the motor and went up to about 27:1

this reads lean right? plugs read lean right?

also read that extrealy rich will "wash" the plugs as well.

well i get about 8mpg. so i was hopeing it was running rich.
but the motor will be most efficient when it is tuned properly right?

any ideas on what jets i should use?
currently running holley 4160 600cfm #66 main jets stock power valve.

motor seems to have more power at part throttle and really no power differiance from half to full throttle.

what are symptoms of a blown powervalve.

im lost guys what way to go?