Chevrolet Repair: 78 C10 fuel sending unit lines, charcoal canister, air vent


Question
Hi there my name is Andrew and I have a question about a 78 Checy c10 delux with a 350 5.7L V8 and Auto trans.  I have replaced the gas tank and sending unit identicle to the one that was on the truck originally and I cannot find where the second smaller line that comes out of the sending unit hooks back up to.  I have the fill line in and the air vent for the fill line in and have hooked up the the larger line out of the sending unit back to the hard line that goes to the fuel pump.  For the life of me I cannot find where the second smaller line connects to the truck. It is connected to the sending unit. Thank you for your time.

Answer
HI ANDREW, THE OTHER SMALL LINE MAY GO TO THE THE FUEL PUMP UNDER THE MAIN 3/8 LINE.. DOES YOUR  FUEL PUMP HAVE ONE LINE OR 2 LINES COMING OUT OF IT ???? IF IT HAS 2 LINES THEN THE SMALL LINE SHOULD GO TO THAT..THAT IS THE RETURN LINE.. IF YOUR PUMP ONLY HAS ONE LINE THEN THIS SMALL LINE IS JUST A VENT THAT SHOULD GO TO A LINE ON THE FRAME RAIL WITH A CK VALVE AT THE OTHER END..A LOT OF THESE TRUCKS DID HAVE A SMALLER 5/16 OR 1/4"..WE KNOW IT IS NOT GOING TO A EVAP SYSTEM,TRUCK IS TO OLD FOR THAT..SOME OF THESE VENTS WENT INSIDE THE HOOD AREA..LIKE A BIG BLACK PLASTIC CHARCOAL CANISTER.CK ALONG YOUR FRAME RAIL FOR ANY BROKEN METAL LINE,IF YOU FIND ONE THIS IS WHERE THIS LINE GOES...LET ME KNOW HOW THIS GOES. IF NO GO, GET BACK TO ME..GOOD LUCK,,TOM...