B230K was difficult to start when petrol evaporates from the carburettor: petrol pump seemed to be not in any problem, yet it will not bring petrol to the carburettor unless the car is started way beyond normal for a car with a dry carburettor??? What is the purpuse and how it works, of the part between the petrol pump and carburettor?

Now it does not want to start at all. If I spray the start-spray or pure petrol through the opening on the carburettor cap (where one of the vacuum hoses is normally connected), it starts immediately and runs few secs, then dies.