Nissan Repair: Fuel consumption for serena, hydraulic tappets, vacuum leak

Question
On average how much  fuel consumption per km should a petrol 2.0 nissan serena fx 1995 automatic do. Mine is doing 7.5km city drive and 10km per litre highway. I hav done all tune ups without help. The exhaust emit s black soot. I hav turned the air mixture screw 2.5 times out like you said but it seems it runs more richer than if l turn it 4times out. Should l turn it out further. Three of my hydraulic tappets are worn out could that be the reason?

Answer
Hello -

The adjustment screw position only plays a small part in the overall settings. It is designed more as a "fine tune". If the car is running rich already, then you probably have deeper issues.

You say the hydraulic tappets are worn, are they noisy? Have you taken a compression test? That would definitely cause the rich mixture. How about locating a possible vacuum leak?

Hope this helps -
aloha
calvin