Fuel and Lubrication Systems Flashcards

What is the primary principle that allows a carburetor's venturi to draw fuel from the float bowl into the intake airstream?

Answer: Bernoulli's Principle

Bernoulli's Principle states that as the velocity of a fluid (air) increases, its pressure decreases. The venturi is a restriction in the carburetor throat that forces air to speed up, creating a low-pressure area that siphons fuel from the higher-pressure float bowl.

In a multi-grade engine oil designation like "SAE 10W-30," what does the "W" stand for?

Answer: Winter

The "W" stands for "Winter" and indicates the oil's viscosity (flow characteristics) at colder temperatures. The first number (10) represents its viscosity when cold, while the second number (30) represents its viscosity at the engine's normal operating temperature.

An engine that uses a splash lubrication system is consistently operated on a steep incline, exceeding the manufacturer's recommended angle. Which type of engine failure is most likely to occur as a direct result?

Answer: Connecting rod bearing failure from lack of oil

In a splash lubrication system, a dipper or slinger on the connecting rod scoops oil from the crankcase to lubricate parts. Operating at an extreme angle can cause the oil to pool away from the dipper, preventing it from splashing oil onto critical components like the connecting rod bearing, leading to oil starvation and failure.

A piece of equipment that was stored for several months with E10 gasoline in the tank now fails to start. The fuel lines appear swollen and soft, and the carburetor is clogged with a gel-like substance. Which of the following is the most likely cause of these issues?

Answer: Phase separation and water absorption by the ethanol

Ethanol is hygroscopic, meaning it absorbs water from the atmosphere. Over time, it can absorb enough water to cause "phase separation," where the ethanol/water mixture separates from the gasoline and sinks. This mixture can corrode metal parts, degrade rubber/plastic fuel lines, and form gums/gels that clog fuel passages.

What is the primary function of the flyweights within a mechanical governor system on a small engine?

Answer: To sense changes in engine speed (RPM)

As the engine speed increases, centrifugal force causes the flyweights to move outward. This movement is transferred through a linkage to the carburetor's throttle plate to maintain a set speed. When the engine slows under load, the flyweights move inward, opening the throttle. Their movement directly corresponds to engine RPM, allowing the system to sense and react to speed changes.

A technician is servicing a commercial-grade V-twin engine and notes it is equipped with an oil filter, an oil pump, and drilled passages in the crankshaft. This combination of components indicates which type of lubrication system?

Answer: Pressure-fed lubrication

A full-pressure lubrication system uses an oil pump to draw oil from the sump and force it under pressure through an oil filter and then through drilled passages (galleries) to critical components like crankshaft and connecting rod bearings. The presence of an oil pump and an external, replaceable oil filter are key indicators of this system.