What is the purpose of changing governor arm length?

Changing the governor arm length primarily serves to adjust the governor's sensitivity. The governor is a crucial component in maintaining the engine's speed by controlling the amount of fuel delivered to the engine based on load conditions. When the governor arm is adjusted, it influences the response of the governor to engine load variations. A longer arm can make the governor more sensitive to engine speed changes, allowing for quicker adjustments in fuel delivery and, consequently, maintaining the desired engine speed more effectively.

This adjustment is particularly important because it directly impacts how the engine responds under different operational circumstances. For example, a more sensitive governor can lead to improved performance by better managing variations in engine load, which may be critical in achieving optimal running conditions. The other options do not accurately describe the primary function of changing the governor arm length, making the adjustment of governor sensitivity the most relevant and correct answer.