The Carburetor Pre-Heater Hose is used to warm the air before it enters the carburetor. 

This is important because warm air is less dense than cold air, which means that it contains less oxygen per unit volume. By warming the air, the carburetor pre-heater hose helps to ensure that the engine receives the proper amount of oxygen for efficient combustion. This can improve fuel efficiency and reduce emissions. 

Additionally, the carburetor pre-heater hose can help to prevent icing in the carburetor during cold weather conditions. Overall, the use of a carburetor pre-heater hose can improve the performance and reliability of an engine.