I don't have a car with acetylene headlamps but I have a basic knowledge of their operation. The fuel chamber is generally filled to normal capacity with the carbide and then sealed up. Open the drip valve just a little to start and then ignite the burner. The valve is then adjusted for the normal flame and generated light. A person has to then adjust it for optimal light output and continuity. This is the part that takes time to get used to. A person can tell you but you need to experience it to get used to it.
The big carbide generators that the A&P school I went to had a regulated feeder that made sure that manifold line pressure didn't exceed 5 PSI. We never had problems with it during oxy acetylene welding classes. It was safer than using bottles of acetylene.