Still pretty new to this forum so I'll go ahead and apologize for any mistakes.
I filled my 20 gallon tank last night to the brim, I could physically see the gas. This morning when I got to a class I'm taking, I noticed that my gas meter was already below the first notch. All in all, since last night when I filled it up, I've driven maybe 10 miles. Is it just me or does it sound like I'm getting very bad gas mileage? I have an eldelbrock air cleaner on the engine and a magnaflow cat along with a thrust muffler. Can someone please give me some advise on how to fix this issue? Thanks in advance!

 

Fill it up. How many gallons went in?

 

I completely filled the tank up. 20 gallons.

 

Again. Fill it up.

Did it take 1 gallon or 5?

How else would you know the gas mileage?