EGR and EFE removal, and what to do with evap canister

WamboJambo

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Hi all,

I'm replacing my intake, exhaust, and carburetor in one fell swoop. As such, I'm working on some emissions vacuum routing to make everything work as expected. Part of that involves exhaust gas recirculation (EGR) and early fuel evaporation (EFE) systems. This topic has been gone over a multitude of times, as any search here (or on other forums) will tell you. I'll try to keep my questions specific to help make this more unique than "should I rip emissions equipment out".

So I've decided to remove both EFE and EGR because my new exhaust (long tube headers) and intake (offenhauser 5416) don't have provisions for the EGR butterfly valve or either of the vacuum valves required, plus I ended up removing the EGR TVS from my water neck because I'll need it for routing coolant to my intake.

Question ultimately is, what do I do with the evap canister? I have no desire to drill a hole in my gas cap, so I'm going to keep the canister there for fuel tank evaporation. There are other hoses though, which go to the EGR valve/TVS, manifold vacuum, PCV valve etc. Can I just plug those ports off and leave it at that?

For implementation-specific details, I'm using ported vacuum from carburetor for vacuum advance to distributor, leaving two other manifold vacuum ports unused (one on carb, one on intake). I also replaced the PCV intake with a breather and sawed the rear PCV valve short to run a hose straight to PCV fitting on carburetor, so there's no longer a need to route that to the canister either.

Here's a copy of the vacuum hose routing for my vehicle for reference; it looks exactly like this stock.
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Thanks for any and all help, and let me know if I should provide any more detail (or go do more research lol)
 

nabeshin

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Route things so that you put spark advance to manifold vacuum. Do not use port vacuum for anything. Your engine will run better if you tune it all to manifold vac.

I believe you can leave the canister connected to manifold vacuum and continue to catch fuel vapors without performance loss.
 

WamboJambo

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Route things so that you put spark advance to manifold vacuum. Do not use port vacuum for anything. Your engine will run better if you tune it all to manifold vac.

I believe you can leave the canister connected to manifold vacuum and continue to catch fuel vapors without performance loss.

Wow! I got things completely backwards, I thought stock used ported vacuum. Thanks a bunch for that tip, will do!

Do you know if it matters if I run the top or bottom hoses to manifold vacuum? Or should I do both and tee it off like shown in the diagram?
 

Catbox

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A most excellent question that I was soon going to research into soon.
I will soon be doing all this to my '79...
So I am following along.
 

nabeshin

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Stock vehicles in the 70s used port vacuum for the advance. It was emissions related.

Check this out, I've seen it linked to around the web:

Post number 2
https://bangshift.com/forum/forum/bangshift/tech-section/32851-ported-vs-manifold-vacuum-advance

I changed my truck from port to manifold vacuum and adjusted timing. I have way smoother idle, and instant throttle response off idle and throughout the rpm range.

I had the thermostatic vacuum tree that would change from port to manifold vacuum when the coolant got too hot, this cooled the engine off because manifold advance makes it run cooler. I took all that off and set everything to run off of manifold vacuum.

Thread about it:
https://www.gmsquarebody.com/threads/vacuum-line-routing.28283/
 

WamboJambo

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So as to not leave people with a dead thread, just gonna go ahead and throw out what I did with it.

Finished the install this weekend, and it seems to run okay like this. Will do some proper timing and touching-up of idle (maybe swapping to manifold vacuum as well like nabeshin recommended) once I get an exhaust on it, since it's so damn loud I can't stand to leave it running more than just enough to warm it up.

I left all plugs on canister wide open except for the fuel tank evap hose, which is still connected. Replaced the EGR TVS with a barb to run coolant to my intake. Replaced the EFE TVS with a plug in the block since I can't use it with my new intake/exhaust combo. Manifold vacuum on intake plugged. Manifold vacuum on carburetor plugged, ported vacuum used for vacuum advance (again, will try swapping those once I get an exhaust fabbed up.

Didn't really notice any fumes from the engine bay which I expected with the canister just exposed to atmosphere, but I also didn't drive it too much, will come back and report in a week or so once I get all this figured out.

Thanks again for the help
 

JoeR Jr

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If you do end up plumbing the EVAP Canister to the carb, it really is best of you use ported vacuum. I also recommend you use a thermostatic switch of some sort. That way you are only purging the canister when it's warmed up, and your foot is on the gas.
If you use manifold vacuum for it, you will be adding fuel vapors to the manifold at idle when the canister is full of vapors, and fresh air to the manifold at idle when it's purged clean. You'd be either richer or leaner than normal all the time. That would make it tough to get the idle mixture correct.
Joe
 

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