Vintage Cars: mpg, engine management system, smog check

Question
i own a 1979 mercedes-benz 280 e and i just got a tune up . the car has 240000 miles and i was wondering if i disconnect the smog pump belt if i would get better mpg .

Answer
Well it will take longer for the catalytic converter and the O2 sensor to reach their ideal operating temperature. It may actually hasten the demise of the catalytic converter. It will take longer for the  engine management system to a achieve a closed loop (as designed). Perhaps you will notice some minor changes in fuel efficiency, perhaps not
IF you have smog check inspections  your car will not pass
Good luck