Gas Mileage eating up!

[JK <jsk2649@osfmail.isc.rit.edu>]

	I have a '73 Automatic that just convertered from Fuel Injection
to Webber 34pct dual carburetor a month ago. I notice the mileage is not
the same as Fuel Injection.
	I would say roughly on my dual carburetor gas mileage would be
like 16 MPG. At around 170 miles, I need to fill it up while on the fuel
injection roughly 240 miles cover the trip. 
	I did not changed the fuel line from fuel injection to carburetor
fuel hose. Would it makes a different? If I changed the fuel line? 
Yes, I did tuned  up the carburetor and the motor is rebuilted.

Please let me know before I start heading back to school pretty soon.
Thanks...