FAA Aviation Mechanic Powerplant (AMP)Fuel, Induction and LubricationMedium
A mechanic is troubleshooting a float carburetor on a reciprocating engine that hesitates and momentarily loses power when the throttle is rapidly advanced from idle. Which component is most likely malfunctioning?
- AThe accelerator pump
- BThe idle mixture adjustment screw
- CThe mixture control cable
- DThe economizer (power enrichment) valve
Show answer & explanationAnswer & explanation
Correct answer: A. The accelerator pump
The accelerator pump provides a momentary shot of extra fuel when the throttle is opened quickly, compensating for the lag in airflow response and preventing a lean-out hesitation. A faulty or worn accelerator pump causes hesitation during rapid throttle advancement.
Why the other options are wrong
- B. Idle mixture affects only idle speed operation, not throttle response.
- C. A mixture cable issue would cause a constant rich/lean condition, not a transient hesitation.
- D. The economizer valve enriches mixture at high power settings, not during throttle transients.
Accelerator Pump
A carburetor component that injects a momentary extra charge of fuel when the throttle is opened rapidly, preventing lean hesitation.
- Prevents lean-out during rapid throttle advancement
- Operated mechanically by throttle linkage
- Malfunction causes hesitation or stumble on acceleration
Memory trick: Accelerator pump = a quick fuel squirt to keep pace with air rush