Author Topic: What to do with fuel lines?  (Read 468 times)

Offline Chuck Step-a-side

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What to do with fuel lines?
« on: March 10, 2018, 09:02:28 AM »
My 1984 Chevy Silverado Stepside was converted from a 305 TBI to 350 4 bbl. before it was purchased by me. The question I have concerning the engine swap has to do with the fuel lines?
On the original 305 TBI with dual saddle tanks; there are the 3/8 fuel line, the 1/8 return fuel line and the 1/8 vapor lines.

What is to be done with the 1/8 return and vapor fuel line when converting to 350 with mechanical fuel pump and Edelbrock 4 bbl?

Should the return lines be blocked off and/or the mechanical fuel pump converted to one without the return outlet or leave as-is?

Is there a fuel line route diagram for 1984 truck with dual tanks?

As always, thank you for your help, Chuck.
« Last Edit: March 10, 2018, 09:05:53 AM by Chuck Step-a-side »

Offline Captain Swampy

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Re: What to do with fuel lines?
« Reply #1 on: March 10, 2018, 09:41:22 AM »
Your 84 had a carb. 87 was the first year TBI was available. Those lines should be connected. IIRC one goes to the fuel pump, the other goes to the charcoal canister. I'm not positive about that. There should be a diagram on the radiator support. Otherwise look in the tech section or hopefully someone else knows and tells you.
1987  350TBI 700R4  4X4  4.56 gears  33" BFG All Terrain

Offline blazer74

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Re: What to do with fuel lines?
« Reply #2 on: March 10, 2018, 01:43:11 PM »
The 1/8 is actually 1/4 return from the fuel pump. The 3rd line is 5/16 which is the canister as mentioned.
The return is not an issue if you have no vapor lock issues.
Vapor lock issues with my 74K5 began with the up to 10% ethanol fuel. I do not have the 1/4 return so I used the 5/16 canister line for my return.
No reason not to have all hooked up as original

Online ehjorten

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Re: What to do with fuel lines?
« Reply #3 on: March 12, 2018, 09:01:20 AM »
3/8" fuel feed line, 5/16" return line, 1/4" vapor recovery line.  The mechanical fuel pump is a 2 line fuel pump with the 5/16" return line.  1/4" vapor recovery goes to the charcoal canister.
-Erik-
1991 V3500 - Gen V TBI 454, 4L80E, NP205, 14 bolt FF, D60, 8" Lift on 35s
1977 K20 Silverado - 350, THM350, NP203, 14 bolt FF, D44, Stock Lift on 31s
1969 Chevelle Malibu Sport Coupe - EFI350, THM350
1968 Chevrolet Step-side Pickup - 300HP L6

Online bd

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Re: What to do with fuel lines?
« Reply #4 on: March 12, 2018, 04:52:58 PM »
Erik, the 1/4" line should be fuel return from the pump to the tank.  The 5/16" line is fuel tank vent to the vapor canister.

Chuck, as Blazer74 pointed out, there are no 1/8" fuel system related lines.  If your truck was converted from carburetion to TBI, and then back to carburetion, take a close look at the line configuration in case it has been altered.
Rich
It's difficult to know just how much you don't know, until you know it....
In other words... if people learn by making mistakes, by now I should know just about everything!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Online ehjorten

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Re: What to do with fuel lines?
« Reply #5 on: March 13, 2018, 09:11:33 AM »
BD...didn't realize they swapped the 1/4" and 5/16" on a carb'ed vehicle.  1/4" is vapor line in FI truck.
-Erik-
1991 V3500 - Gen V TBI 454, 4L80E, NP205, 14 bolt FF, D60, 8" Lift on 35s
1977 K20 Silverado - 350, THM350, NP203, 14 bolt FF, D44, Stock Lift on 31s
1969 Chevelle Malibu Sport Coupe - EFI350, THM350
1968 Chevrolet Step-side Pickup - 300HP L6

Offline VileZambonie

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Re: What to do with fuel lines?
« Reply #6 on: March 13, 2018, 09:41:03 AM »
To my knowledge the standard was:

carbureted 3/8" supply, 5/16" vapor, 1/4" return

EFI 3/8" supply, 5/16" return, 1/4" vapor

I'm sure there are variables for different configurations.
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