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Evaporation Control System
https://slantsix.org/forum/viewtopic.php?t=68719		 Page 1 of 1
Author:  SpeedBanana1977 [ Wed Aug 05, 2026 6:20 pm ]
Post subject:  Evaporation Control System
Hi all--
I recently purchased a 1972 B100 Sportsman shorty van with a Slant Six. Near the back door is the vertical metal canister for the evap control system. There are four lines from this canister to the gas tank; my understanding is these run inside the tank to each of the corners. There's a fifth line from the canister to the driver's side of the engine bay. I'm pretty clear on how this is "supposed" to hook up, but what I'm wondering is if I could delete the metal canister and use one of the vent lines to connect to a charcoal canister (as detailed elsewhere on this site) in the engine bay and use another to connect to a vapor return line on a three-pronged fuel filter. The other two vents would get connected together with a loop of fuel hose.

I'm not opposed to putting the whole thing back to original, but I'd rather not have that metal can in the van when I want to use it as a camper.
Author:  SlantSixDan [ Thu Aug 06, 2026 12:41 pm ]
Post subject:  Re: Evaporation Control System
All the info you need is here.
Author:  SpeedBanana1977 [ Thu Aug 06, 2026 2:38 pm ]
Post subject:  Re: Evaporation Control System
Thanks Dan! I used that article successfully on my 1980 Volare some years ago now. Is it worth the effort to employ another one of the four tank vents as vapor return line connected to a three pronged fuel filter?
Author:  SlantSixDan [ Thu Aug 06, 2026 6:19 pm ]
Post subject:  Re: Evaporation Control System
Quote:
Thanks Dan! I used that article successfully on my 1980 Volare some years ago now. Is it worth the effort to employ another one of the four tank vents as vapor return line connected to a three pronged fuel filter?
Well…h'mm. Interesting question. Your vent would be blocked when nose-up or nose-down with a full(-ish) tank, and there are probably other reasons why this isn't such a hot idea; I'd have to think it through. The existing single vent line coming off your existing metal canister would be ideal to connect to the 3rd nipple on the fuel filter, and while you then wouldn't delete that canister, you'd still get the advantages of using a proper charcoal can to store fuel vapours instead of using the engine crankcase.
Author:  SpeedBanana1977 [ Thu Aug 06, 2026 8:55 pm ]
Post subject:  Re: Evaporation Control System
Thanks! I think I'll start out by running one of the four vents to the charcoal canister and capping the other three. Will skip the three prong fuel pump for now (does not seem to be easy to find, anyway) as well as the three prong fuel filter.

I think it's worth noting that the Napa purge valve is still availabke but it's now running around $40 US plus shipping!
Author:  hyper_pak [ Fri Aug 07, 2026 6:42 am ]
Post subject:  Re: Evaporation Control System
Dan, is there a replacement charcoal filter element for the 76 style canister?
Author:  SlantSixDan [ Fri Aug 07, 2026 2:06 pm ]
Post subject:  Re: Evaporation Control System
Quote:
I think I'll start out by running one of the four vents to the charcoal canister and capping the other three
This is not a good idea, don't do it this way. They didn't just eliminate three of the tank vents the following year ('72 on passenger cars, '73 on trucks); the reason why they were able to go to a single vent line from the tank and no 4-into-1 liquid/vapour separator is that the internal shape of the tank was changed to provide a permanent air pocket at the vent line location, even with a full tank. The previous tanks don't have that, and you'll get liquid fuel in the vent line – very ungood; you don't want this.

Keep the 4-into-1 can, and run its single output line to your (new) charcoal can, instead of to the crankcase via the breather with the extra nipple (install a standard breather without extra nipples).
Quote:
Will skip the three prong fuel pump for now
You wouldn't want this; this is for setups that use the crankcase rather than a charcoal can to store the vapours.
Quote:
as well as the three prong fuel filter
You would want this, for better hot-engine starting/idling/driveability – especially on your van, with its notoriously hot engine compartment exacerbating exactly those problems.
Author:  SlantSixDan [ Fri Aug 07, 2026 2:10 pm ]
Post subject:  Re: Evaporation Control System
Quote:
Dan, is there a replacement charcoal filter element for the 76 style canister?
The cans don't have a charcoal filter element. They're just full of granular activated charcoal, held in by screens. Some of the cans have a replaceable air filter element, a round disc of batting material on the underside of the can, held in by being slid in between the can and a cross-strap. Those filters are readily available.

Charcoal can rebuild: see here
Author:  hyper_pak [ Fri Aug 07, 2026 6:30 pm ]
Post subject:  Re: Evaporation Control System
Thanks
Author:  SpeedBanana1977 [ Mon Aug 10, 2026 11:34 am ]
Post subject:  Re: Evaporation Control System
Thanks Dan! I'm starting to see the light! I'll keep the metal canister (it's way back in the corner, anyway) and run the output line from that to a charcoal can . . . and on down the line per your article mentioned earlier.

What plumbing would be necessary to connect that three-prong fuel filter?
Author:  SlantSixDan [ Wed Aug 12, 2026 12:36 pm ]
Post subject:  Re: Evaporation Control System
Fuelproof 1/4" hose from the filter's 3rd (vapour) nipple all the way back to tee into that single vent (output) line coming off the metal canister. Route it so there are no dips in this run of hose. Likewise, no dips in the hose from the carb bowl vent to the underhood canister.
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