Fuel efficiency issues Options

[brandon702bmx]

Recently on my 1994 Celica, I swapped the engine for a younger 5S. I've noticed that I'm getting terrible fuel economy. I would fill my car about $10.00 @ $2.53-70/gal. Like the other day, I filled at $2.53/gal, $10.00 = about 4 gals. I only get about 60, 70-80 miles out of that. I know that isn't right because even at 80 miles I'm getting 20 miles a gallon. Any ideas where I should look for the culprit? I realize the car is 23 years old, but I would prefer to get better mileage out of it. It's suggested 27 city, 43 highway. I am quite leadfooted but even then I don't believe it should be THAT bad.