Fuel sending unit question

[kychevy]

Guys, I am sorry if it’s been asked b4 but I’m a little stumped with the fuel sending unit. 87 TBI and adding 2nd tank that was removed. Bought the crossover lines and had new tank plumbed but then took a look a look @ passenger tank and the 1/4” line is the vapor line. Reason I state this is the crossover lines I bought from LMC has the 5/16” metal line as the vapor. I was under impression 3/8 was feed, 5/16 was return and 1/4 was vapor…..is that wrong? That metal line has me 2nd guessing myself now.

 

[kychevy]

@Ronno6 The correct sizes are
Fuel line 3/8"
Return line 1/4"
Vent line 5/16"
So your truck is setup correctly. Whatever the other thing you read was wrong.

So, I finally found this but another question is why is my pollak selector valve 3/8” and 5/16” if 1/4” is the return?

 

[SquareRoot]

I just went thru this converting my 85 to EFI. Replaced the entire system. The 1/4 is the vent. 5/16 is return. The 6 port Pollack valve has 5/16 and 3/8 barbs. The vent lines t into each other and run to the vapor cannister .The vent line does not go thru the valve. The 3/8 has one input and two outputs (left or right tank). Same with the return, thus 6 ports. Is this an 87 factory TBI truck with fuel pumps in the tank? Earlier trucks with a carb and mechanical pump are slightly different, don't confuse the two.

 

[kychevy]

I just went thru this converting my 85 to EFI. Replaced the entire system. The 1/4 is the vent. 5/16 is return. The 6 port Pollack valve has 5/16 and 3/8 barbs. The vent lines t into each other and run to the vapor cannister. Is this an 87 factory TBI truck with fuel pumps in the tank?

Yes it is. It’s kinda a Frankenstein truck and thought had it figured out but started seeing other info so threw me off little bit. Thanks for the reply

 

[SquareRoot]

Yes it is. It’s kinda a Frankenstein truck and thought had it figured out but started seeing other info so threw me off little bit. Thanks for the reply

See my edit for added clarification.

 

[SirRobyn0]

Yes it is. It’s kinda a Frankenstein truck and thought had it figured out but started seeing other info so threw me off little bit. Thanks for the reply

I could be misremembering the lines, also my truck is carbureted. thanks Mike @SquareRoot for correcting the line info.

 

[ali_c20]

I installed new sending units on my 74 c20.
Without return: Fuel line 3/8" Vent line 5/16"
With return: Fuel line 3/8" Return line 1/4" Vent line 5/16" is the setup for the carb trucks.

When you look at the sending unit the vent line has some kind of valve thingi on it.

https://www.gmsquarebody.com/threads/dual-tank-questions.1567/

 

[SirRobyn0]

I installed new sending units on my 74 c20.
Without return: Fuel line 3/8" Vent line 5/16"
With return: Fuel line 3/8" Return line 1/4" Vent line 5/16" is the setup for the carb trucks.

When you look at the sending unit the vent line has some kind of valve thingi on it.

https://www.gmsquarebody.com/threads/dual-tank-questions.1567/

Ok thanks so I did have that right.