What is the correct fuel consumption for a 1.8litre laser

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Hi
I have a 1994 Laser and currently get about 9.7litres per 100km.

It used to be 8 litres per 100km. Exactly the same way to work each day and it has steadily dropped over the 30 000 ks I have done.

Could not changing plugs account for the fuel consumption increase???? What should I get??? The cars done 230 000km.

thanks