What would cause a peugeot 405 - 1.6l engine have high fuel consumption?

The carb has an automatic choke, this is fed with coolant through thin pipes to the carb to heat it up and so switch it off when the engine warms up. Check the pipes are not blocked, and check that the thermostat on the choke unit has not failed. If it is a late car with fuel injection, check the water temp sensor. Good luck...............