225 drinking lots of fuel?

Hey everyone,
I finally was able to do a test run this weekend since Ive noticed my dart has been taking a lot of fuel.
I filled her up, drove 117 miles (pure highway) and she drank 3 quarters of a tank.
I haven't had the chance to go fill her up yet but i wanted an idea on if anyone thinks this is normal for the 225 ( my gut is telling me no, its not normal ).
I leaned out the carb as much as i could, checked for leaks, tires are good... I Have the Pertronix kit on it, and her timing at the moment is 10 degrees, i gaped the plugs at 35 if my memory serves me right.
I'm wondering if i should invest in an air fuel gauge so i can see exactly whats going on with my mixture.
If anyone has any ideas or could even tell me if this is normal for this engine that would be great, please bare in mind i am fairly new to this engine and carburetor ( Holley 1920 ).
Thanks !