73-87 Chevy _ GMC Trucks > Fuel Systems and Drivability

new 20 gallon tank

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Rough75C20:
Hello All,

Looking to upgrade my C20 Fuel system. I currently have a 14-gallon tank on the passenger side that is being used as the main tank. However, the sending unit isn't hooked up to the gauge so I'm guessing on gas level right now. I am looking at getting a new 20-gallon tank from Jegs. Question is about the fuel sending unit. the truck currently has a 305 with a 4-barrel Quadrajet. I'm looking at the fuel sending units and I believe I need the one with two outlets (supply and vent). I haven't seen a return line to the current tank. Is this normal for these old carb setups? I have attached what is currently in my shopping cart from Jegs. Let me know your thoughts. I'm planning on using a T with a ball valve to control which tank is being used, but the sending unit will be hooked up to the main tank.

Captkaos:
73-87's only came with 16 or 20 gallon tanks, not 14.
Are you talking about adding an additional 20 gallon tank or replacing the existing 16 gallon tank?  Why not just fix the sending unit in the tank?
For the T/ball valve how are you going to do the Vent line?  I am unsure what the question is on the supply/send?  Can you elaborate?

Rough75C20:
Hello,

Thanks for the reply. I believe the original tanks were pulled and whatever the previous owner had was put in on the passenger side, could be 16 gal. It is currently on the passenger side with the cap sticking out of the side of the bed. I would like to have a tank that actually uses the fuel door on the driver's side and my thinking was, I might as well get the 20-gallon tank since I have a long bed. So, I would bw adding an additional tank. Honestly, I'm not even sure where the vent line "vents" to. does this go to somewhere else on the engine? can it just be open or plugged off? Can the line be spliced into the vent line of the other tank? The question on the supply / send is there are two different sending units on Jegs for my year of truck. there is a 3 port and a 2-port sending unit. one has a return port as the third port, and the other one doesn't. I'm not sure how you know which one you need. I don't know if my truck needs a return line to the tank or if only needs a supply to the carb.

JohnnyPopper:
Do a search here or elsewhere for fuel and vent line diagrams. You want to get this right or other gremlins will come to the party... :( :(

Captkaos:
Generally speaking it vents to atmosphere, OR a charcoal Cannister/engine.  I would find out what you have on the opposite tank and make it match, being a C20 it is possible it only used the 2 port but I would check.
You don't want to vent one tank back into another tank.  Some of these also had vented caps, but no idea on the year.  You dont want to cap it off as the tank will pressurize.

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