#21  
Old 06-29-2020, 09:16 AM
PontiacJim1959 PontiacJim1959 is offline
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Here is what I have from one of my Pontiac repair books. May help?
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  #22  
Old 06-29-2020, 08:01 PM
tjs72lemans tjs72lemans is offline
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Thanks for all the info and insight. PontiacJim, thanks for the diagram. I looked in my manual and have that. So, the A body stand pipe allows for the tank to vent. My issue is, I did not have and was not planning on using the purge valve that would've been in my intake. I installed an after market thermostat for a gauge there. If I were to run the canister to the carb port, it would be sucking vapors at all times and possibly messing with my idle. If this line to carb was left open to the atmosphere and hanging down by frame, it could still vent fumes I assume, but maybe smell a little at times when parked. Am I wrong or is there a better way around this without the purge valve in intake?

  #23  
Old 06-30-2020, 09:28 AM
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I have run mine open at the canister for 20 years and have never noticed any vapor from it. Just plumb it down by frame like your asking and its fine.

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Old 06-30-2020, 05:55 PM
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Originally Posted by tjs72lemans View Post
Thanks for all the info and insight. PontiacJim, thanks for the diagram. I looked in my manual and have that. So, the A body stand pipe allows for the tank to vent. My issue is, I did not have and was not planning on using the purge valve that would've been in my intake. I installed an after market thermostat for a gauge there. If I were to run the canister to the carb port, it would be sucking vapors at all times and possibly messing with my idle. If this line to carb was left open to the atmosphere and hanging down by frame, it could still vent fumes I assume, but maybe smell a little at times when parked. Am I wrong or is there a better way around this without the purge valve in intake?
On my chevelle, I have no purge valve on the intake at all.

Only hoses to the engine........I simply run the 3/8 hose through the PCV as pictured which goes over to the base of the carb.
Then the little vacuum line runs along with it, also to the carb, and is ported vacuum at the metering block (holley carb) to trigger the vacuum switch on top of the charcoal canister. That's it.

It absolutely has no affect what so ever on idle or part throttle cruise. My air fuel ratios are very steady and spot on.

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Old 06-30-2020, 08:58 PM
tjs72lemans tjs72lemans is offline
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I don't think my canister has a switch in it. It is flat on top and if I blow into it, it takes air and not plugged. One person mentioned if running all the time, it would create too much vacuum for the tank and cause a problem. Not sure if that can happen with the stand pipes. Maybe they allow enough source for excess vacuum so as not to suck the tank in. I thought the stand pipe would allow atmospheric air pressures to fill the tank as needed.?

400 Lemans, thank you for that insight.

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Old 06-30-2020, 09:10 PM
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My Formula doesn't have a visible switch on top of the canister either. It's hooked up in a similar fashion, a vacuum line and 3/8 hose to the carb. There is no purge valve on the intake of that one either.

As far as I know, both systems on my Chevelle and Firebird run all the time, they've never created too much vacuum at the tank or created any kind of issue. In fact without the tank venting the opposite problem occurs. Remember the vacuum connection is switched (ported) at the carb so it's not active at idle anyway. Matter of fact, I would think you'd want it functioning most all the time anyway, because a tank that isn't vented at all causes way worse issues than a charcoal canister ever will. I've had that issue before and fuel delivery becomes a nightmare.

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Old 07-01-2020, 09:56 AM
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The carb port for the vent is not a true vacuum port, it's much weaker than that and doesn't pull much vacuum at all (stick a vacuum gauge on it and see). You can unplug it and it won't cause any trouble with the engine idling. On the 2 port canister cars, it doesn't pull a vacuum on it and just captures the fumes passively. On '72, the only time they didn't want it functioning was before the engine had fully warmed up as it increased emissions ever so slightly - obviously not enough to keep the system in later years.

The standpipe vent at the tank in '69 vented the fumes to the atmosphere and in the name of reducing emissions and reducing smells of gas, they closed the venting system more and more as the years went on.

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Old 07-01-2020, 10:47 AM
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On my 71 A-Body, I run the vent line from a Tanks Inc EFI tank to the standpipe/separator at the top of the diff house/trunk/back seat. I do a 'Y' connector on the one line from the tank vent, the other end, one goes into the 'tall' vent tube, the other goes to the 'drain back' tube.

Same setup on my 71 'bird and 72 442.

No vapor/fuel smell from mine.

The Tanks Inc vent is a POS, it leaks like heck, especially when you have a full tank and slam on the brakes. Throw that thing right in the trash.




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  #29  
Old 07-01-2020, 11:07 AM
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The Tanks Inc vent is a POS, it leaks like heck, especially when you have a full tank and slam on the brakes. Throw that thing right in the trash.




.
Agree 100% I had the same issue with those things. The biggest problem is that I simply couldn't mount it high enough. Even above the rearend in the tunnel I couldn't get them mounted higher than the filler neck on the tank. So with a full tank of gas, and hard braking, it leaked, even parking on an incline caused it to leak. Total garbage.

I found that if the car doesn't have the charcoal canister vent system (like our 69Z) the easiest way to vent the tank is with a simple vented cap, and to even get one of those that worked properly I had to buy an NOS cap. The repops suck.

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Old 07-01-2020, 11:14 AM
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Originally Posted by Ben M. View Post
The carb port for the vent is not a true vacuum port, it's much weaker than that and doesn't pull much vacuum at all (stick a vacuum gauge on it and see). You can unplug it and it won't cause any trouble with the engine idling. On the 2 port canister cars, it doesn't pull a vacuum on it and just captures the fumes passively. On '72, the only time they didn't want it functioning was before the engine had fully warmed up as it increased emissions ever so slightly - obviously not enough to keep the system in later years.

The standpipe vent at the tank in '69 vented the fumes to the atmosphere and in the name of reducing emissions and reducing smells of gas, they closed the venting system more and more as the years went on.
On my 70 Formula, with the Quadrajet, the canister is actually a 3 hose system. One is like you said, a vent to the carb, not a vacuum assist. But it does have a smaller 3/16" hose hooked to vacuum on the carb. A 3rd hose going to the tank. However no visible switch on top of the canister.

Odd how these systems vary from year and model throughout their use. 2 hoses, 3 hoses, vacuum switches, no vacuum switch.

You make an important point on the 72 comment and not wanting to work until the engine warmed up. That's why the vacuum hose that ran from the switch to the carb runs through a thermal switch on the intake first, that triggers vacuum at a certain temperature. This switch was also used for things like vacuum advance.

I bypassed that on my 72 Chevelle and no longer have the thermal switch installed so the charcoal canister works full time. I've had it this way for the last 35 years with no ill affects.

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Old 07-01-2020, 11:25 AM
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I've found that vented caps do not offer enough venting for most requirements, and any mods to the cap make them spit out on WOT.

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  #32  
Old 07-01-2020, 11:49 AM
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Originally Posted by HWYSTR455 View Post
I've found that vented caps do not offer enough venting for most requirements, and any mods to the cap make them spit out on WOT.
I guess it would depend on how much fuel you're feeding the engine?

I don't know, dad's GTO is the stock 69 vent system, which isn't much, but we found that to work fine with a 571 and 724 hp using a 400 lph walbro pump in the tank. He's went from carb fuel pressures to now 60 PSI with a Holley stealth EFI unit, and it's been great.

I'm just using the stock charcoal canister as a vent on my 72 chevelle with a 600hp 454, and the same 400 lph walbro pump in the tank. It's working fine.

A real NOS vented cap will in fact leak a little fuel on WOT launch if the tank is full. That's a normal deal. The repop stuff doesn't and I think that was part of the fuel feeding problem with those things, they didn't work quite like an original vented cap, and today I don't think they are allowed to make them that way anymore. That's why I bought an NOS piece for our Camaro.

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Old 07-01-2020, 09:26 PM
tjs72lemans tjs72lemans is offline
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Thanks. Once I fire the broke in engine in the car, I will check the vacuum on the port. If it is minimal, I may try to just run full time.

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Old 10-03-2022, 05:10 PM
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I've heard some folks use the newer suburban one, but have no feedback on that yet.

https://www.amazon.com/Vapor-Caniste...934Y4F85&psc=1

I've been hooking my tanks to the the OE separator over the diff, letting it air to the outside, and not had any issues with smell, have done that for years, seems to work, even on hot days with the car in the garage.

But guess it would be better to have a charcoal one, so have been keeping an eye out for options.

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Old 10-04-2022, 07:30 AM
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I've never had any vapor smell issues with any of the cars vented right to atmosphere and they all get parked in the garage. The nomad, Camaro, goat, and the bug all vent straight through the fill cap. 3 of them sit in the same shop and combined I still don't have fuel vapors in there.

I'm not super clear on how one gets to that point other than it must be building up some serious pressure when parked??

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  #36  
Old 10-04-2022, 08:41 AM
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Yeah, not sure how that works, where some have the smell and others don't. I know I had my LeMans venting directly to air with one of those Tanks Inc rattle vents, and not only did that thing leak bad, it smelled bad too, even when it wasn't leaking. Just by hitting the brakes that thing would gush.

I ran the vent line temp to the OE separator and boom, smell gone. And that thing vents to the air.

Same thing on the 442, used a diff rattle vent (which it too leaked), went to the OE setup venting to air and it's good.

I remember doing homework on it and looking for alternate solutions, but didn't think the cost of some of them were 'fair'. Even thought about making one out of an overflow tank, but realized the separator was working for me.



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  #37  
Old 10-04-2022, 09:01 AM
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Originally Posted by HWYSTR455 View Post
Yeah, not sure how that works, where some have the smell and others don't. I know I had my LeMans venting directly to air with one of those Tanks Inc rattle vents, and not only did that thing leak bad, it smelled bad too, even when it wasn't leaking. Just by hitting the brakes that thing would gush.

I ran the vent line temp to the OE separator and boom, smell gone. And that thing vents to the air.

Same thing on the 442, used a diff rattle vent (which it too leaked), went to the OE setup venting to air and it's good.

I remember doing homework on it and looking for alternate solutions, but didn't think the cost of some of them were 'fair'. Even thought about making one out of an overflow tank, but realized the separator was working for me.



.
Yep that's pretty much what I've found so it just has me curious how some have a vapor smell issue.

One thing I discovered on those aftermarket rattle vents after talking to a couple people, they had been using them but rather than run a simple line to a high point under the car, they are running a coiled line to it.
So basically the vent line has 4 or 5 coils in it on it's way to the rattle vent. I guess in an attempt to keep raw fuel from sloshing up to the vent, especially when the tank is full.
I've been experimenting with that method but thought that was an interesting point to share.

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Old 10-04-2022, 09:11 AM
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I tried a few coils of line on the 442, the tank slosh when braking easily overcame it, still gushed. I had it hanging right off the OE separator, so it was high enough.

I dunno, if I run into the prob again, and with the separator config, will just add a charcoal can off the separator and be done with it.


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  #39  
Old 10-04-2022, 09:14 AM
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I tried a few coils of line on the 442, the tank slosh when braking easily overcame it, still gushed. I had it hanging right off the OE separator, so it was high enough.

I dunno, if I run into the prob again, and with the separator config, will just add a charcoal can off the separator and be done with it.


.
Yeah the jury is still out with my experiment. It was just something I wanted to try for future purposes and to maybe see if it helps or changes anything on the big in tank pump in any way.

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  #40  
Old 12-07-2022, 03:39 PM
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I haven't had any issues here in Arizona. I have both cars with charcoal cannisters and older cars before charcoal cannisters became a thing with just a simple vented cap. Never any fuel smell from any of them.

I will say, and not sure I mentioned it before as this is an old thread, on the older cars that use a simple vented gas cap, I searched out NOS caps for those cars as the repop stuff you buy, or the caps sold in stores don't seem to work properly.
It appears to me they only sell post 1970 caps that say "vented" but they technically are really the caps designed for the charcoal cannister cars.

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