| Fuel vapor separator plumbing [message #355154] |
Tue, 26 May 2020 16:10  |
winter
Messages: 247
Registered: September 2007
Location: MPLS MN
Karma: 0
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I'm redoing my vent lines and have a routing question. On my 77, the bottom port of the separator goes to the charcoal canister and the lines from the tanks come in the top port. Seems like it should be the other way to let liquid drain back to the tank.
Which way is the correct plumbing?
Thanks
Jerrod Winter
1977 Palm Beach
Green Jelly Bean
Twin Cities, Minnesota
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| Re: [GMCnet] Fuel vapor separator plumbing [message #355156 is a reply to message #355154] |
Tue, 26 May 2020 16:40  |
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It's right. It's to keep fuel out of the canister and air into the tanks.
bdub
On Tue, May 26, 2020, 4:11 PM jerrod winter via Gmclist wrote:
> I'm redoing my vent lines and have a routing question. On my 77, the
> bottom port of the separator goes to the charcoal canister and the lines
> from
> the tanks come in the top port. Seems like it should be the other way to
> let liquid drain back to the tank.
>
> Which way is the correct plumbing?
>
>
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bdub
bdub.net
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| Re: Fuel vapor separator plumbing [message #355169 is a reply to message #355154] |
Tue, 26 May 2020 21:33 |
Rick Staples
Messages: 126
Registered: May 2014
Location: Johnstown, Colorado, USA
Karma: -1
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Senior Member |
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Winter wrote: "I'm redoing my vent lines and have a routing question. On my 77, the bottom port of the separator goes to the charcoal canister and the lines from the tanks come in the top port. Seems like it should be the other way to let liquid drain back to the tank. "
Jerrod,
You are correct. The separator's function is to prevent liquid fuel from reaching the charcoal cannister when filling the tanks. It has little to do with venting during fueling, as that is done by the hose back to the filler neck. The service manual has no good info about this, but if you look closely at the diagram in the 78Z parts book (page 12-2, top right) you can see the routing.
The lower chamber of the separator has a plastic ball that will float in gasoline. If the lower chamber fills up with gas, the float ball will rise and block the passage to the top chamber. When the gas drains back down to the tanks, the vent is reopened to the upper chamber and thence to the charcoal cannister. The pent roof of the separator goes up when mounting it.
HTH
Rick Staples
Rick Staples, '75 Eleganza, Johnstown, CO
"Advice is a dangerous gift, even from the Wise to the Wise, and all paths may run ill." -Tolkien
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| Re: Fuel vapor separator plumbing [message #355188 is a reply to message #355154] |
Wed, 27 May 2020 17:20 |
winter
Messages: 247
Registered: September 2007
Location: MPLS MN
Karma: 0
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Senior Member |
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Thanks for the info. Looking close at the diagram my suspicion is correct. The top line goes to the charcoal canister and the bottom to the tanks. Previous owner plumbed that wrong at some point and it's been backwards for the 20 years I've had it.
Probably a good idea to replace the canister now as well
Jerrod Winter
1977 Palm Beach
Green Jelly Bean
Twin Cities, Minnesota
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| Re: Fuel vapor separator plumbing [message #355192 is a reply to message #355154] |
Wed, 27 May 2020 18:43 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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No need to replace canister as well. Just the filter element at the bottom. Like $3. They purge when engine runs.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Fuel vapor separator plumbing [message #355193 is a reply to message #355192] |
Wed, 27 May 2020 19:14 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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But you do need to remove the vapor separator and shake it. If
the "ping-pong ball" inside rattles, the unit is probably OK; the most
common failure is the housing distorting and binding the p-p ball. You
should also turn it upside down and blow on the bottom (now top) port to be
sure the needle valve, moved by the p-p ball, seals. If there's been no
leakage from the valve, it should work as well as a new one. DO NOT do
what I did the first time I fooled with one: I put compressed air on it to
check the needle valve. The glued-on top section blew off so that I could
examine the innards of the thing. I glued it back together. That lasted a
few years before it began to leak. I then reinforced it with some Lexan
and an aviation hose clamp. That was probably 15 years ago and it still
works.
Ken H.
On Wed, May 27, 2020 at 7:44 PM John R. Lebetski via Gmclist <
gmclist@list.gmcnet.org> wrote:
> No need to replace canister as well. Just the filter element at the
> bottom. Like $3. They purge when engine runs.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
>
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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