What are the main causes of vapor lock in fuel systems?

Vapor lock occurs when the fuel in the system changes from a liquid state to a vapor state, which can prevent the fuel from reaching the engine effectively. The primary causes of vapor lock are high fuel temperature and turbulence. High temperatures can increase the fuel's vapor pressure, promoting the formation of vapor bubbles, while turbulence can disturb the flow of fuel, causing localized areas where vapor is more likely to form due to drops in pressure.

Understanding the effect of these two factors is crucial because when the fuel is heated, particularly in areas close to the engine where excess heat can transfer to the fuel lines, the risk of vapor lock increases. Additionally, turbulence can arise in the fuel lines due to bends or restrictions, further complicating the fuel delivery system's efficiency.

The other options mention factors such as low fuel pressure, high altitude, or excessive turbulence, without correctly linking them to vapor lock causes, or they introduce conditions that are less likely to directly affect vaporization in the fuel system, making them less relevant to the problem at hand.