FAA Powerplant Written Practice Test 2026 – Complete Exam Prep

Question: 1 / 1165

A hissing sound from the carburetor during manual propeller pulling indicates what?

Vacuum leak

Intake valve blow by

A hissing sound from the carburetor during manual propeller pulling indicates intake valve blow-by, which is a situation where a portion of the combustion gases escapes from the combustion chamber into the intake manifold due to an inadequate seal between the valve and its seat. This can happen if the valve margins or seats are worn, preventing a proper seal when the valve is closed. The hissing sound is the result of pressure escaping, and it can indicate a problem with the integrity of the intake system.

Understanding this condition is crucial for maintaining engine performance, as any loss of compression can lead to a reduction in efficiency and power output. It's important for a mechanic to properly diagnose this sound to determine if valve adjustments, seat replacements, or other corrective actions are necessary to restore proper function.

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Fuel vaporization

Oil starvation

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