Why does my 1991 Honda Civic DX eat so much gas?

[AiRtRaCk B]

I have replaced spark plugs and changed oil. Does it take a few days or miles for the good oil to kick in? Or is there still something else wrong with it?

 

[joshman06us]

did you replace the air and oil filters, the actual spark plugs, and the plugs to the cap to the sparks, is there a leak in the fuel tank?