BUILD THREAD “The Juggernaut”

Rktpwrd

Builder of Cool Shjt
Supporting Member
Feb 2, 2015
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Calgary, Alberta, Canada
So, if a charcoal canister is present, wouldn't that mean the cap is not vented?

I don’t honestly know. Maybe, maybe not. I’m open to learning, so someone please educate me. Perhaps worthy of a separate post to the general forum to ask?

Regardless, even if it isn’t a vented system in stock configuration, I don’t see any reason why it couldn’t be converted to vented style with the addition of a vented cap. Nothing else is stock on this car, so why should the fuel system be any different.
Lol
 
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Built6spdMCSS

Geezer
Jun 15, 2012
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Florida Beach
On my 1984 SS the line going to the Charcoal Canister up front was 5/16" steel line on the driver's side of the frame. I used it for my EFI return line when I did my build.
 
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Built6spdMCSS

Geezer
Jun 15, 2012
5,694
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Florida Beach
So, if a charcoal canister is present, wouldn't that mean the cap is not vented?
Cap would not be vented because it has to be a closed system.

I'm really trying to remember how the stock one was with the stock sending unit because the 1/4" line in there was the Carb return if I remember right. The 5/16" was the EVAP vent that is in the top of the Sending Unit. On my car that 1/4" runs up front with the 3/8" feed, I use the 1/4" currently as the tank vent.

The non charcoal Carb stuff I've seen is 2 line Sending Units, 3/8" feed & 1/4" return.
 
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Supercharged111

Comic Book Super Hero
Oct 25, 2019
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Colorado Springs, CO
Cap would not be vented because it has to be a closed system.

I'm really trying to remember how the stock one was with the stock sending unit because the 1/4" line in there was the Carb return if I remember right. The 5/16" was the EVAP vent that is in the top of the Sending Unit. On my car that 1/4" runs up front with the 3/8" feed, I use the 1/4" currently as the tank vent.

The non charcoal Carb stuff I've seen is 2 line Sending Units, 3/8" feed & 1/4" return.

A return line for a carb? Is that at the pump then?
 

scoti

Royal Smart Person
Sep 5, 2019
1,959
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Texas
I know that 1/4" goes all the way to the front passengers side and comes out of the frame. Someone here with one still hooked up stock can chime in where it's hooked to.
I'll look. I have an '81 Elky flipper project I picked up @ the end of Nov '22. The smog equipment charcoal canister/assorted hoses were missing so we used the bare space for a 1.5gal fuel tank while trouble-shooting the engine issues. I recall seeing the hard line there (driver side rail). I'll look @ it again & see where/how far it goes back. Never occurred to me to compare it to what's on my '78 Bu.
 
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clean8485

Comic Book Super Hero
Dec 18, 2005
2,860
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Ontario, Canada
I ran into this issue a few years ago. I have 2 different A/G bodies. One is a 1984 Monte SS, and the other is a 1980 Malibu. When I bought the Malibu, in the process of getting it running, I replace the fuel pump. The Malibu has a 2 line fuel pump, inlet from the tank, and outlet to the carb. I had the carb for the car rebuilt, and after the repairs, I had an issue with fuel literally flooding out of the carb. I thought it was a problem with the carb, but the rebuilder told me that he had seen this problem before. He suggested that first, I try gravity feeding the carb, and seeing if the car ran OK, which it did.. He told me that there are 2 different fuel pumps for a SBC, and they operate at different fuel pressures, because they have different diapragms in them. As he explained, there's a fuel pump with 3 lines on it, and a deeper bowl. One of the lines on that pump is a return line to the tank, because that fuel pump operates at a higher fuel pressure. My Monte SS has the 3 line pump on it, and there are 2 lines that run along the right side of the frame-a pressure line and return line. The Monte still has a separate line along the left side of the frame, that goes to the charcoal vapour canister. The carb rebuilder told me that a 2 line pump runs at 6-7PSI of fuel pressure, while the 3 line pump runs at about 10-11PSI, which is too much fuel pressure to the carb, unless there's a return line, which bleeds off the excess fuel pressure. He said that he had seen (in rare cases), where a 2 line pump had a 3 line diaphrapm in it, making it run at higher fuel pressure, which will cause the carburetor to flood. He told me to get another fuel pump, from a different supplier, and try it on the Malibu. I did. Long story short, end of problem. Never seen that ever before, but its the truth.
 
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69hurstolds

Geezer
Supporting Member
Jan 2, 2006
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You will need a vented cap to make this particular setup work. Cars with their EVAP systems intact use a non-vented cap from the factory. I ALMOST mentioned it the other day, but figured you had that taken care of as you pretty much have three steps ahead already planned out.

It's true, on Oldsmobiles with Oldsmobile V8 engines with the canister, the canister vent line ran from the two or three connections at the tank pickup (that third connection was for fuel pump return line if applicable) and immediately made a left turn at Albequerque and over to the driver side. After all, the tank was vented into the front of the wheel well on our cars with canisters and didn't need a vented cap. The vent pipe ran along driver side until the rear of the engine cradle/crossmember and up along top of the frame on the passenger side. If it was on the "wrong" side, like Chevies.... :) ...j/k... it was left alone on the left side and didn't cross back over since the canister was on the driver side. So if your car used to have a canister, you may remember taking off that line somewhere in the past. If not, it still could be up in there.
 
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