FAA Powerplant Written Practice Test

What should be done when a new carburetor is installed on an engine?

1. Immediately adjust the idle speed

2. Adjust the idle mixture first, then the idle speed

3. Run the engine without adjustments

4. Only check for leaks

The correct answer is: Adjust the idle mixture first, then the idle speed

When a new carburetor is installed on an engine, the recommended approach is to first adjust the idle mixture before adjusting the idle speed. This sequence is crucial because it ensures that the engine runs smoothly and efficiently. Adjusting the idle mixture involves fine-tuning the ratio of air to fuel at idle, which is vital for optimal combustion and engine performance. If the mixture is too rich or too lean, the engine may not idle properly, leading to stalling or rough operation. Once the idle mixture is set correctly, adjusting the idle speed becomes effective, as the engine will now have a stable fuel-air mixture to work with. This sequence of adjustments helps prevent the risk of having to re-adjust the idle speed if the mixture isn't set first. It creates a more systematic approach to establishing the engine's idle characteristics, ultimately contributing to better throttle responsiveness and fuel efficiency. Other options may imply incorrect practices, such as adjusting the idle speed without ensuring that the mixture is correct first or running the engine without any adjustments, which could lead to operational issues or potential damage to the engine. Checking for leaks is certainly a necessary step after installation, but it does not replace the need for proper adjustment of the carburetor settings, which is essential for optimal