Which fuel line should be opened when bleeding the fuel system?

When bleeding the fuel system, the correct approach is to open the line at the highest point. The reason for this is that fuel systems can trap air, which can lead to poor performance or the engine not starting. By opening the line at the highest point, any air trapped in the system can escape more easily. This allows fuel to flow freely, ensuring that the air is purged from the system effectively.

Positioning the bleed valve at the highest point helps facilitate the removal of air bubbles, which tend to rise. The fuel from the lower sections of the system will push upward, aiding in pushing the air out. Therefore, this method is critical for ensuring that the system is fully primed and free of air before operation.

In contrast, opening lines at the lowest or middle points may not effectively clear the air out, as those positions do not take advantage of the natural tendency of air to rise. Similarly, the line nearest to the fuel tank, while it can be important for maintenance, may not effectively serve the purpose of bleeding the system in the most efficient manner.