Better mpg for 91 protege?

[91protegeDX]

right now i am getting about 26mpg out of my 1.8L sohc protege and i'm reading the ppl are getting in the 30 mpg range and some say they put on high flow cats and high flow mufflers.will doing that up my mileage?
and if anyone can answer this last question that would be great,i can go 200 miles on half a tank but after that the mileage like disappears and mpg goes down the drain and after another 100 miles its about time to fill up,so i can go like a little ofer 300 miles on a tank but i can go 200 miles on just half a tank where i should really be able to go 400 miles on a tank,whats wrong here?

 

[11B-33T]

I have a stock cat connected to a Magnaflow (forget the model right off) on my 92 LX. On the hwy I average +/- 28 to 30 but that's also using cruise @80-85mph. City driving is about 24-26 average so you're in the ballpark.

Don't have the manual in front of me but I believe we have a 14.2 gallon tank and the the lo fuel light comes on when you've two gallons left in the tank. Are you filling up when you're on vapors or when the low fuel warning is on?