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.
Plain English
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.
Context Anchor
Seen during engine starting, especially when using a manual fuel primer before turning the starter.
Derivation
From 'over-' (too much) plus 'priming,' which in engine use means giving the engine an initial shot of fuel to help it start. So overpriming literally means giving it too much of that starting shot.
Why Pilots Care
Overpriming causes hard starting, risks spark plug fouling, and can delay departure or require extra clearing procedures.
Grounding Statement
Picture pumping the primer too many times, then trying to start the engine while extra fuel is still sitting in the engine’s starting path.
Intuition Check
More primer is not always better. The primer is only meant to add enough fuel to help the engine start, not to soak it with fuel.
Example Sentence 1
On a cold morning the pilot used three primer strokes as the checklist specified, careful to avoid overpriming the engine.
Example Sentence 2
Clearing the engine after overpriming requires mixture at idle cut-off and several propeller turns before attempting another start.