FAA Powerplant Written Practice Test

How is the oil and gasoline mixture delivered to the carburetor in two-stroke cycle light sport aircraft engines?

1. By electric fuel pumps

2. By gravity feed or oil injection systems

3. Through vacuum lines

4. Using pressurized tanks

The correct answer is: By gravity feed or oil injection systems

In two-stroke cycle light sport aircraft engines, the oil and gasoline mixture is delivered to the carburetor primarily through gravity feed or oil injection systems. This method is effective due to the inherent design of two-stroke engines, which rely on a continuous flow of the fuel mixture for proper operation. Gravity feed utilizes the force of gravity to draw the oil and gasoline mixture from the fuel tank down into the carburetor. This is a simple and reliable method, especially common in smaller aircraft where complex fuel pump systems may not be necessary or desirable. On the other hand, oil injection systems can also be employed in these engines to ensure that the correct amount of oil is mixed with the fuel at all times. This system automates the mixing process, improving efficiency and reducing the possibility of an incorrect ratio that might occur with manual mixing. Both methods are aligned with the operational needs of two-stroke engines, which require a consistent mixture to maintain proper combustion and lubrication. Therefore, this choice accurately reflects the mechanisms involved in delivering the oil and gasoline mixture to the carburetor in such aircraft engines.