fuel efficiency

Thank you TC Forum for letting me join your feed. Curently own a 98 Lexus GS300 and apart from the fuel consumption a beautifully tailored ride. Love to get my hands on a water cooled carburator....circa 81. Back soon D.s

I'm interested in old cars. Not necessarily vintage cars but the cars from 70's, 80's and some even 90's. However, the problem is with their engines. They devour gas like an ogre. Like having a mileage of just 8km/ltr. I want to know what are some modifications that can be applied to these...