Evap (charcoal) Canister Hookup help

[goathearder]

Ok, I just got my new Evap (charcoal) canister and I am a bit confused how to hook it up.

There are 3 ports:
1) Tank - obviously connects to the tank vent link
2) Fresh air - connects to nothing
3) Purge - Confused on this one

From my research, it looks like the purge line connects to the carb vacuum line but this is where I am getting confused. If I block the tank port, leave the fresh air port open and apply vacuum to the purge port, it just sucks air in from the fresh air line, it won't hold vacuum. So if I connect a vacuum port on the carb to it, won't I just have a giant vacuum leak? (Its an edelbrock 1825 Thunder AVS carb).

Is the carb really where that purge line is supposed to connect?

 

[British Slave]

On mine, with TBI it's hooked up like so:
One hose goes to the fuel tank. The small fitting goes to a tee in the PVC valve hose, and the other vacuum hose goes to the front base of the TBI unit. There is a filter on the bottom of the cannister that needs to be serviced also.
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[kyrow]

Can you guys post a picture of the canisters you are using? I am confused on this same issue. I have an 85 carburetor system that I have yanked most all of the emissions related hardware off. After plugging all the ports on the canister (except for leaving the hose to the fuel tank) I have a problem where the fuel tank generates too much pressure. It causes problems with difficulty starting as though the heavily pressurized system forces fuel into the system causing flooding. If I leave the has cap off, it starts like a champ (fumes, air, etc. rush out verrrrry noticeably when the cap is removed). Don't even have to touch the gas pedal. Fires right up. The canister I have in there right now has six ports, one of which has the fuel hose that runs to the tank. The rest are capped off. Maybe I should invest in a new one like you are talking about goathearder.

I am not trying to rob this thread but am interested in contributing. I have tried searching but come up short with finding much info on this subject. Thank you for any info.

 

[dyeager535]

The 1991 manual is obviously talking about TBI, but I *think* in operation it should be similar.

The purge line is hooked to a "timed" (ported) vacuum fitting on the TBI (or carb obviously). So yes, it IS a vacuum leak, but not at idle.

Kyrow, this is the only photo I could find semi-quickly online: http://www.google.com/url?sa=i&rct=...cVMz7qIPQtsamtCBFB39AZQw&ust=1361857125552025 that is a purge valve. Not to get too much into it, but again, I'm guessing you have something like that attached to the top of your canister? The top fitting is hooked to a timed vacuum source, and when the throttle is opened, should then open that valve, letting whatever it controls (either vapor from tank or vacuum from motor) flow through.

I'm kind of surprised that with everything plugged it doesn't "vent", I'm surprised it will hold that much pressure. But in any case, if you have enough vacuum ports, running a ported vacuum source to the fitting on the valve, should get you started on the right path to getting it operational again. With 6 ports it's going to be somewhat difficult to figure out which is which, but whatever is marked "purge" should be the one that gets manifold vacuum.

I could be completely wrong, as the carbed emissions setups got very complex. If your core support sticker is still there, I believe that will tell you how everything was hooked up, and in my experience you can eliminate any thermal controlled vacuum valves/switches without noticing too much of a problem.

 

[goathearder]

Ok, so i should probably t off my ported source and run it to vac advance and the canister. That makes sense.

 

[British Slave]

Pic here:

http://coloradok5.com/forums/showthread.php?t=304487


This is just like my 87.

 

[dyeager535]

Yep, that's the photo I was thinking of. The top fitting on that valve should go to a ported vacuum source. Not how it was probably done with a carbed setup (with 6 ports there were probably all sorts of thermal switches and what not) but the ported source will keep it from being a vacuum leak that hurts idle.

 

[hillbilly deluxe]

http://coloradok5.com/forums/showthread.php?t=304487 looks just like my '73.

Got me curious so I got some pics of mine. 73 with Q-jet. Mine has 3 ports, very easy to figure out. Labeled: Fuel tank, PCV, Carb. My PCV port is plugged and always has been since I bought the truck. I wonder how that is affecting it?

Don't the newer engines have PCV as well? Maybe "Purge" is like PCV and "Fresh Air" goes to the carb?? Just guessin

Top view, middle is plugged PCV.

Carb

Fuel Tank

 

[dyeager535]

My guess is it's plumbed wrong. The "carb" one is probably timed and/or thermally controlled vacuum, the "PCV" was probably tee'd into the PCV line and fed the vapors into the carb that way.

I'm not saying GM couldn't possibly have run a cap, but having seen how that valve is used to control purge on other canisters makes me suspicious in your case.

 

[hillbilly deluxe]

Oh yeah, I wasn't trying to assert that mine is correct, just that it was always like that. I doubt it was capped from the factory.

 

[dyeager535]

Well they did some weird stuff, you never know!

Just looked at the evap canister in my car, and even though it's from the 80's and was carbed, it only has two fittings on it. Tons of vacuum lines elsewhere though. Go figure.