1974 Fuel lines, size and number????

[kanuck]

As I am pretty much putting a 1974 truck together, (1974 cab and front end, 73-80 frame and parts from where ever), I was wondering what I need for fuel lines.
I kept a set from a 1984 short box I disassembled for a pattern to bend my new ones, but it has 3 lines running back towards the tank. Two seem to go from the mechanical fuel pump back to the tank, (one 3/8 and one a bit smaller) and another one from the drivers side rad. support back, (charcoal canister??).
If I am building this with plans for a strong 400 to 500 HP engine, (still contemplating small block verses big block), what fuel lines will I need as I have no pollution inspection and I am not worried about a stock rebuild.
Planning to keep a mechanical fuel pump, unless I run into problems with that idea.
Have bought a fresh gas tank and am running it on the passenger side, but am reusing the old float and sender unit that I removed from a 1980 short stepside.
Thanks for any info you can give me.
Hagen

Frame being assembled


Cab being prep for re-assembly with frame. Only rough spot is inside rockers

[kanuck]

Hi,
No suggestions????
Single line?
Double line for a return?
Get rid of the charcoal canister? (don't know if it was even there in 1974)

Also, I think the rad suport is different on the 73-80 then the 81-87?
Is the a quick way to ID the early one, as I have kept 3 or 4 rad supports and want to use the right one.
Will be using the 1974 grille assembly when finished. Can I use a hood lock cable or do I have to keep to the hood lever from outside only???

Thanks

[MalibuSSwagon]

Short breakdown of the lines on my 86 truck:

3/8" supply
1/4" return
5/16" vapor line.

The 5/16" line is the one that runs to the driver side.

[kanuck]

Do I have to run all the lines or can I eliminate the vapor and return lines?

How about the rad support question?

Anyone???

Thanks

[walkerb]

My 74 doesnt use a canister and it was built in Canada. But it is a 250

[Jonboy]

Seems like you are on the right track. The 3/8 is the fuel supply line. On my '74, it ran under the engine mount tower and doubled back. The line going towards the drivers side is the charcoal canister; there was one on my '74 (federal emissions).

[ray_mcavoy]

Originally Posted by kanuck

Do I have to run all the lines or can I eliminate the vapor and return lines?

How about the rad support question?

Anyone???

Thanks

Hi kanuck,

You can eliminate the 5/16" vapor line, but you'll need to leave that port on the sending unit open in order to vent the gas tank. Some trucks (over a certain GVW) came from the factory without vapor canisters and on those trucks GM simply installed a vent cap (like the ones used on transmissions/rearends) onto the vapor line fitting of the sending unit.

I believe the purpose of the 1/4" return line is to help prevent vapor lock. So keeping that might be a good idea. As you noticed, this (along with the 3/8" feed line) hooks to the mechanical fuel pump.

As for the radiator supports, the 73-80 ones use a separate bolt-on top panel that serves as a hood latch mount and fills the gap between the top of the radiator support & grille. I think that top panel is all stamped as one piece with the 81-up radiator supports.

There was an inside hood release option from 77-80 that you could use if you can find all the necessary parts. I think it'll work okay with the 74 grille you're planning on using.