Plain English Meaning

Pumping too much fuel into the engine before starting it. The engine ends up with more fuel than it can burn cleanly, which makes it hard to start and can be a fire risk.

Full Definition

The act of injecting too much fuel into the engine intake using the primer before starting, resulting in an excessively rich fuel-air mixture in the cylinders and intake manifold. Overpriming can wash lubricating oil from cylinder walls, cause hard starting, and create a fire hazard if raw fuel pools in the induction system or drips from the carburetor.

Context Anchor

Seen during engine starting, especially when using a manual fuel primer before turning the starter.