fuel consumption slc350
 

I bought a 350SLC from 1978 very recently. So far everything seems to be ok, the only thing I am worried about is fuel consumption. While on the highway the car consumed around 11l/100km, in the city it went up to 25l (which is around 9.5mpg in the city and 21.5mpg on highway). Is that normal? If not, do you have any suggestions what could be a possible problem?
thanks for your help

Tune up?
 

Maybe a good tune up would help fuel mileage increase some?

-George