My jeep is very hard starting when left for a day or two without being started. Seems as if the fuel drains from the carb. In tracing the fuel from the fuel pump I find my fuel filter has one line in from the fuel pump and two lines out, one to the carb and one that appears to head toward the rear of the jeep. What is the line heading to the rear for? Is hard starting a common problem on this engine (4.2L)?