1985 4x4 Fuel System

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Paul texas

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Paul
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1985
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1500
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305
Guys,
I am new to the group and could use some help. I just bought a 1985 Chevy Silvardo SWB step side that "had" dual tanks, Im starting from scratch, have new tanks and sending units installed . Have bought the fuel selector valve(6port), now im stuck and need help on how to run fuel lines, have 6 ports on selector(1 supply to fuel pump and 1 return), kinda know how lines go. But coming off sending unit there are 3 lines. Not sure on the 3rd line. Man any pics or advise would be greatly appreciated. Its a 305, manual fuel pump
Thanks
Paul
 
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Chuckd84

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Chuck
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Silverado K20
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I think one of the 3 hose barbs on the sending units is the tank vent. Should be a few inch long hose with a plastic vent on the end. You can look at the unit out of the tank to determine the suction and return ports. If i can find an old one in my shop ill post a pic showing which one is what
 

Old Guy Bill

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The 3/8” port is fuel supply to carb, the 1/4” port is fuel return from mechanical fuel pump, the 5/16” port is tank vent, it originally went to charcoal canister.
 

Paul texas

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The 3/8” port is fuel supply to carb, the 1/4” port is fuel return from mechanical fuel pump, the 5/16” port is tank vent, it originally went to charcoal canister.
I found in a manual the selector and it looks like" 3/8" is the supply to the fuel and the 5/6" is the return, but i am not sure at all. This should be so simple, maybe just over thinking it
 

Old Guy Bill

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Over the years Chevy had many different versions of fuel systems.
There are several different styles of pumps and sending units available also.
Pumps can have one or two ports. Sending units can have one, two, or three ports.
Only the fuel supply and return lines route through the tank selector valve.
The tank vent lines can be run to a charcoal canister or just left open.
 

Paul texas

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Caldwell Texas
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Paul
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1985
Truck Model
1500
Engine Size
305
Over the years Chevy had many different versions of fuel systems.
There are several different styles of pumps and sending units available also.
Pumps can have one or two ports. Sending units can have one, two, or three ports.
Only the fuel supply and return lines route through the tank selector valve.
The tank vent lines can be run to a charcoal canister or just left open.
Thanks
 

Paul texas

Junior Member
Joined
Dec 7, 2023
Posts
4
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Location
Caldwell Texas
First Name
Paul
Truck Year
1985
Truck Model
1500
Engine Size
305
Question: off the fuel sending unit there are 3 port 3/8, 5/16, and 1/4. I assume the 3/8 is supply but of the other 2 which is return? To me it looks like the 5/16 would be the return???
 

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