Refer to figure.
The priming system includes a priming pump that injects fuel into the induction manifold to help start the engine.

Its primary function is to deliver extra fuel to the intake ports of the cylinders.

In the absence of a priming system, additional fuel can be supplied to the cylinders by pumping the throttle lever, which activates the accelerator pump to provide more fuel.

The priming pump operates alongside the main fuel pump (which may be electric or mechanical), drawing fuel from the filter housing and directing it to the inlet manifold.

The amount of priming needed depends on the ambient temperature and the duration since the engine was last run. Priming is usually required for the first flight of the day and in cold weather if the engine has been idle for several hours, though sometimes the engine may start without priming.

Over-priming an engine, especially a hot engine can cause excessive fuel to accumulate in the cylinders, leading to potential issues such as:

• engine flooding,
• increased risk of engine fire, and
• fouling of the spark plugs