Fuel Injection - explain this to me like I am 6 years old

So how is it you have a totally stock 318 with a 4 bbl? A 71 318 had a 2 Bbl Carter BBD. What intake and carb are you running?!?

As other have mentioned, your MPG is way low. You may think it is running "fine" but there is probably room for improvement. Things to look at:
First: VACUUM ADVANCE is it hooked up, and does it work?
Second: Mechanical advance. Does it?
Third: Static timing. What is it set at, and is the mark on your damper any where close to reality?