Small Gas Engines Chapter 8 Test

The carburetor must meet five different engine running conditions: cold or hot starting, idling, part throttle, acceleration, and high speed operation. These conditions require the carburetor to provide the correct fuel-air mixture to ensure smooth and efficient engine performance. During cold or hot starting, the carburetor must provide enough fuel for easy ignition. During idling, the carburetor must deliver a stable fuel-air mixture to maintain a steady engine speed. Part throttle and acceleration require the carburetor to adjust the fuel-air mixture to provide the necessary power without causing engine hesitation or bogging. Finally, during high-speed operation, the carburetor needs to deliver the right amount of fuel to ensure optimal performance and efficiency.

The three basic types of carburetors are natural draft (side draft), updraft, and downdraft. These terms refer to the direction of air flow in the carburetor. In a natural draft or side draft carburetor, the air flows horizontally into the engine. In an updraft carburetor, the air flows vertically upwards into the engine. In a downdraft carburetor, the air flows vertically downwards into the engine. These different types of carburetors are designed to accommodate different engine configurations and optimize air-fuel mixture for efficient combustion.

The correct answer explains the three basic functions of governors. They maintain a speed selected by the operator within the range set by the governor, preventing overspeeding. Additionally, they limit both high and low speeds, ensuring safe and efficient operation of the engine. This answer is clear and directly addresses the question.

The correct answer is 15 to 1. This ratio indicates that for every 15 parts of air, there is 1 part of fuel in the mixture by weight. This ratio is commonly used in internal combustion engines to ensure proper combustion and efficient fuel consumption. A higher air-to-fuel ratio promotes complete combustion, reducing emissions and improving fuel efficiency.

The needle valve in the carburetor float chamber is responsible for controlling the flow of fuel. It needs to be made from materials that are durable and resistant to corrosion. Neoprene is a common material used for the needle valve as it is flexible and can withstand exposure to fuel. Brass is also commonly used as it is a strong and corrosion-resistant metal. Both neoprene and brass are suitable materials for the needle valve in the carburetor float chamber.

The correct answer is oil-wetted, dry types, and dual element. These three types of air cleaners are commonly used to remove impurities from the air. Oil-wetted air cleaners use oil to trap and filter out particles. Dry types rely on a dry filter media to capture dust and debris. Dual element air cleaners have two filters, typically a primary and secondary filter, to effectively remove contaminants from the air. These three types provide different options for air purification depending on the specific needs and preferences.

The governor spring is attached to the throttle lever in a governor installation. This spring is designed to open the throttle valve. When the governor senses that the engine speed is too low, it pulls on the throttle lever through the spring, causing the throttle valve to open. This allows more fuel and air to enter the engine, increasing the engine speed and maintaining the desired speed. Therefore, the governor spring's purpose is to open the throttle valve.

The safest solution to wash an air cleaner plastic foam element is detergent and water. Detergent is a mild cleaning agent that can effectively remove dirt and debris from the foam element without causing any damage. Water helps to rinse away the detergent and any remaining dirt, leaving the foam element clean and ready for use. Using gasoline or kerosene to clean the foam element can be dangerous as they are highly flammable and may cause damage to the plastic foam.

The barometric pressure decreases as altitude increases. Since 3500' MSL is higher than 1500' MSL, the barometric pressure at 3500' MSL would be lower than 29.95". Therefore, the correct answer is 25.95" Hg.

During starting, the engine requires a rich air-fuel mixture to facilitate the combustion process. This is because the cold engine needs more fuel to start and run smoothly. As the engine warms up, the air-fuel mixture is gradually adjusted to a leaner ratio for optimal performance and fuel efficiency. Therefore, the richest air-fuel mixture occurs during the starting phase of the engine.

The load adjusting needle regulates the amount of fuel that enters the main discharge nozzle on certain carburetors. This needle controls the flow of fuel based on the engine's load, adjusting the fuel-air mixture to optimize performance. By fine-tuning the amount of fuel entering the nozzle, the load adjusting needle ensures that the engine receives the appropriate fuel supply for efficient combustion.

The correct answer is flat pleated paper cartridge filter. This type of air cleaner is the newest for small gasoline engines. It is designed with a flat pleated paper cartridge that effectively filters out impurities from the air before it enters the engine. This type of filter is efficient and provides better air filtration compared to the other options mentioned.

A diaphragm carburetor has the advantage of being able to incorporate a fuel pump diaphragm. This means that the carburetor can deliver fuel more efficiently and consistently to the engine, resulting in smoother operation. The fuel pump diaphragm helps maintain a steady flow of fuel, preventing fuel starvation and ensuring optimal performance. This is particularly beneficial in high-performance engines or situations where a consistent fuel supply is crucial.

When the engine is idling, it means that it is running at a low speed without any load or significant power output. During idling, the engine's acceleration well fills up, which suggests that the engine is not producing enough power or torque to generate acceleration. This is because idling typically involves the engine operating at a low RPM (revolutions per minute), resulting in a slower speed and less force being generated.

The correct answer is air vane (pneumatic) and centrifugal (mechanical). Small engine governors are responsible for controlling the speed of the engine. An air vane governor uses air pressure to regulate the engine speed. It consists of a vane that moves with the airflow generated by the engine and controls the throttle accordingly. On the other hand, a centrifugal governor uses weights and springs to respond to changes in engine speed. As the engine speed increases, the weights move outward, which in turn reduces the throttle opening to maintain a constant speed.

The choke valve in the carburetor is always located nearest the intake end of the carburetor. This is because the choke valve is responsible for controlling the amount of air that enters the carburetor during cold starts. By placing the choke valve near the intake end, it allows for easier control of the air-fuel mixture and ensures that the engine receives the necessary amount of fuel to start and run smoothly in cold conditions.

During idle and fast idle conditions, the main discharge nozzle is inoperative. This means that it is not providing any fuel to the engine. Instead, the fuel is being supplied through other channels or jets. The main discharge nozzle is typically used during higher engine speeds when more fuel is required. However, during idle and fast idle conditions, the engine is running at lower speeds and therefore does not require the additional fuel from the main discharge nozzle.

The diaphragm in a carburetor draws fuel during a vacuum pulse from the manifold or crankshaft. This means that when the engine is running, a vacuum is created in the intake manifold or crankshaft, which causes the diaphragm to move and draw fuel into the carburetor. This fuel is then mixed with air and delivered to the engine for combustion. This mechanism allows the carburetor to regulate the fuel flow based on the engine's needs, ensuring proper fuel-air mixture for efficient combustion.

The carburetor economizer is a device that reduces float bowl pressure, which in turn reduces the amount of fuel discharged into the venturi. It operates only after the engine reaches part throttle. Therefore, all of the given options are correct explanations for the carburetor economizer.

The updraft carburetor would normally require a smaller air passage than the other two types because it is designed to have the air flow from the bottom to the top, against gravity. This design allows for better fuel atomization and mixing, resulting in improved combustion efficiency. The smaller air passage helps to create a stronger suction effect, drawing the fuel up into the carburetor and ensuring a proper fuel-air mixture.

In a venturi, the air pressure is least where the velocity is greatest. This is because according to Bernoulli's principle, as the velocity of a fluid increases, the pressure decreases. In a venturi, the narrowing of the pipe causes the air to accelerate, resulting in a higher velocity and lower pressure. Therefore, the air pressure is least where the velocity is greatest.

Air bleeds are small openings in the fuel system that allow air to mix with the fuel. This process helps to improve the atomization of the fuel, which means breaking it down into tiny droplets for better combustion. By improving atomization, air bleeds ensure that the fuel is evenly distributed and efficiently burned, leading to better engine performance and fuel economy.

The correct way to clean an air filter cartridge of the pleated paper type is to shake it external side down. This method allows any loose dirt or debris to fall off the filter, ensuring that it is thoroughly cleaned. Soaking it in kerosene or blowing it clean may not effectively remove all the dirt and could potentially damage the filter. Shaking it external side down is the recommended method for cleaning this type of air filter cartridge.