My car will vapor lock in extreme heat gas line is insulated . why does it do this?

Vapor lock can only happen in a suction type fuel delivery system, that is when the fuel pump is located near the engine.

High temperature causes the fuel in the line to turn to vapor in a vacuum environment and the pump cannot pull the fuel past the air pocket. ( pump loses suction at the air pocket )

Modern fuel pumps are located in the fuel tank which eliminates the problem completely.

If you do have a fuel pump that is not located in the tank the line is most likely passing close to a heat source somewhere between the pump and the tank, there will be no issues from the pump to the carburetor since it is a pressure or pump type after the pump and any air will be pushed by the fuel behind it.