When bleeding a fuel system, when should you close the bleed valve?

When bleeding a fuel system, the appropriate time to close the bleed valve is when air-free fuel is flowing. This is crucial because the purpose of bleeding the system is to remove any trapped air that could hinder the proper operation of the fuel system. Air in the fuel line can cause performance issues, such as loss of power or engine misfires.

By waiting until you see a steady stream of air-free fuel, you ensure that all air has been purged from the system, allowing for proper fuel delivery. This action helps establish an unobstructed fuel pathway, ensuring that the engine receives a consistent and reliable fuel supply once the system is returned to operational status. Closing the bleed valve prematurely, before confirming that the fuel is free of air, could lead to operational issues down the line due to residual air in the fuel system.