Reasons for low fuel efficiency for 1990 geo metro

[vikasintl]

We have 1990 automatic geo metro 3 cylinder 1 liter where head is recently changed and recent full tune up but mileage is only 25 mpg.
What could be the main reason why fuel economy is bad?
One mechanic said timing belt other said timing needs adjustment...am confused.
What are the main possible reasons?
is it a easy fix or it is just because it is old?

[Frank Lee]

Something was missed during the "full tune-up".

There are so many possibilities it would be onerous to list them all.

Maybe the guy that did the "tune-up" should look at it again.. for free.

[Ryland]

yeah, sounds like a bad tune up, unless the tranny is shot, alinement is way way off, or something else that the mechanic found and should have told you about.
granted with the automatic you are not going to get the best mileage, still mid 30's

[RobertSmalls]

I would usually blame this on the driver and the weather, but when your fuel economy is that bad, Frank is right, something (could be almost anything) is probably wrong with the car.

[Johnny Mullet]

The head was rebuilt for a reason, so I suspect a clogged cat.