fuel problem with a 1972 dodge dart

Over 80K miles is "getting there" if the engine has never had any work. Could be that the timing chain/ sprockets is worn badly and maybe even off a tooth by now

Minimum I'd do a compression check, and check the tuneup to be sure the timing is OK, and that the mechanical and vacuum advance are not failed

With over 80K, it could have some bad valves. Check the heat riser butterfly that it's not stuck, and that the choke is not stuck shut.

How about your driving? Even if you drive carefully, if most of your driving is slow around town stuff (to school, etc) it won't get very good mileage, and...

how about short trips? Let's say your ride to school/ work is short, it has little time to warm up

Here's a complete 72 shop manual that was posted not long ago, you can download for free.

http://www.forabodiesonly.com/mopar/showthread.php?t=132309&highlight=manual,+download