My cousin's new-to-him '86 K10 with a 305 has a dying fuel pump. He has 2 parts trucks, another '86 K10 with a 305 and an '84 K20 with a 350. All 3 trucks are carbureted. We were looking at his fuel pump last night and it has a third fuel line which I assume is a return line? Is the pump internally bypassed? We looked at his other 2 trucks to salvage a pump from them and they have the same mechanical pump with 3 lines. I assume the big line is from the tank, the smaller line is the return and obviously the metal line goes to the carb (through a new clear fuel filter we installed with 2 small pieces of flexible fuel hose) Why does the pump I put on my '84 K20 only have the 1 feed line to the pump and the 1 line to the carb? Sorry, I've been into my Cummins diesels for 9 years now and just getting back into the gasser world. I didn't think carbureted motors needed a return line. Thanks.