us marine

Ok I am reworking some of the vacuums lines and i have 3 coming from that vapor canister towards the driver front fender. 1 small and 2 a bit bigger.

I think the small one goes to the front of my Edelbrock Performer Carb (smaller inlet) the other 2 I have no Idea!

Do I even need to have these or can I block them off. Car seems to run fine with them plugged.

Any pictures or diagrams would be great.

gingerbreadman1977

i got rid of mine a long long time ago . if you dont need to pass inspections then im all for getting rid of that coffee can and other stuff. everyone gives me heaps of fury for throwing out my ccc and components out of my 81 but i dont care.... it was the best move i ever made.

the big one comes from the tank and you can either block it off in the engine bay or at the back.the other from memory goes to the polution pump but watch out the greenies will be telling you off for killing the environment soon.

us marine

Ahaha thank GBREAD Im just gonna block that junk off. When I get some time probably take it out. But do you get strong fuel odors from your car now?

gingerbreadman1977

nope no vapours at all. ...well actually no more than i used to have .

TedH

My vapor canister actually failed. It stopped trapping/sending the fumes back to the gas tank. I replaced that set of vacuum hoses and the canister with new components from Dr Rebuild and never had another problem. If the lines get blocked off, just be sure that your system isn't going to vent the fumes (from your carburetor opening) into your garage (if it is an enclosed space). Those fumes can collect and be a hazard. At a minimum, they pose an environmental impact since fuel vapors are considered harmful to the environment.

The vapor canister has no ill effect on performance. If I recall correctly, it is an effective means of routing the vapors back to the fuel tank. I believe one of the lines that runs from the canister goes back to the fuel tank. I just checked my Dr Rebuild schematic and my evap canister has five or six connections depending on your application. There is a center post on the top of the canister that routes back to the fuel tank. The 'tubes' described on the GM diagram for the replacement evap can from Dr Rebuild:

Control Vacuum Tube
PCV Tube

Fuel Tank Tube - routes vapors back to the tank.

Air Tube (Fresh Air Inlet) - There is a splash cap on this tube from GM. Depending on whether your system uses the splash cap, either retain or remove if you get a new canister.

Manifold Vacuum Tube
Carburetor Bowl Tube

larryg3

If it does not hurt performance and is out of sight and reduces the risks of accumulated vapors why eliminate???

BTW i too removed the air pump just so that the engine bay looks cleaner.

Mark G

I personally wouldn't do that. It was all put there for good reason, partly environmental, also for operational. Most people, like a buddy of mine rip that stuff off cause they don't understand it ...sometimes even at great cost of time and $$ to make run right with older technology (even though the problem could stem from a faulty $50 part or bad connector). My buddy spent lots of time tracking down and buying parts to replace his former computerized car system, had to reinstall a bunch of things ...only to loose about 4 mpg and the thing still doesn't run for crap. The best thing anyone with an 81 can do is get the GM CCC manual, which you can usually find on Ebay for a couple bucks, and read up on it. It fully explains how all the emission parts work together in easy to understand language ...and their importance and theory. Demystifies the CCC system. Also explains the rest of the CCC electronics, the carb and how to troubleshoot and test the various components with multimeters and test lights.

The CCC system and the electronic controlled carb is a computerized engine management system, somewhat like a simple fuel injection system that meters fuel. When tuned up, it will give you great idle and fuel economy that you won't have to constantly readjust like a typical carb. Your car won't fill your garage with fumes either like a carb will. The charcoal canister is still available from GM. RockAuto has them. If you swap in a larger engine and go for high performance then you probably do want to rip it out. I also have an 81 Caprice that I drove the wheels off for years. It ran great using the same system as the 81 Vette.

Mark G

RobertHuggins

Be careful here. This is part of a complete system that includes venting the gas tank. If you eliminate the charcoal canister entirely, then you need to vent your gas tank.

You do not want to eliminate the charcoal canister, plug up all of the lines, and keep the non-vented gas cap. If you do that, you will build pressure in your gas tank. The weakest point will vent the pressure.

How much pressure and how quick depends on what type of fuel pump is on the engine. The original post was for a 1981 that has the fuel pump that returns warm fuel back to the gas tank. That design builds pressure quick.

What I don't understand is all 6 of the fittings. Which are inputs? Which are outputs? which are both?

The "FUEL TANK" is an input of gas fumes from the gas tank.
The "PCV" is an output of those gas fumes into the carb. But only when there is vacuum applied to the purge valve.
the "CARB BOWL" is an input of gas fumes from the carb bowl. But only when there is NOT vacuum applied to the valve on top of that fitting.
The 6th fitting on the 1981 charcoal canister is the vent. Marked "AIR CLNR" and routed thru a 3/8" hose to the air cleaner. This vent seems to be an input or an output depending on whether the car is running and/or how much pressure is building in the gas tank. On other cars, the vent is just a hole in the bottom of the Charcoal Canister.

I do not understand what these gas fumes do to the rich/lean mixture when vacuum is applied to the purge valve. Apparently it does make the mixture rich and thus vapor lock could occur.

If the smog equipment on your car has deteriorated with age and it is impossible or imparactical to maintain the original design, I suggest that you do not plug the "AIR CLNR" fitting if you keep the "FUEL TANK" fitting hooked to the gas tank and you keep the non-vented gas cap.

There has to be some type of vent somewhere for the gas tank.

SGAL1

Please excuse my ignorance....but what does CCC stand for?
It sounds like I need this book. I would like to learn all of this.
I am in the process of re-hosing my emissions/vacc system in my 81. Thanks...

larryg3

CCC is Computer Command Control and the '81 was the first vette to have a computer to control the fuel/air ratio (carb) first and only vette year with this carb not counting the california emission vette in '80, and the timing (Distributor) as well as the lock up converter in the trans. th350C (also first and only year for the vette)

SIXFOOTER

Here is the schematic for the 81 vac system emission controls.
Depending on what mods you have done, some can be eliminated.
For instance, if you have installed dual exhaust and deleted the Cat, then you do not need the AIR pump and can eliminate the EFE/TVS and block the T on the white hose on the drawing.
Besides an operational canister, the Purge TVS needs to work, it allows the evacuation of the canister with the engine up to operating temp.
The only horsepower robbing component is the AIR pump and I think its only something like 2hp max. The EGR is a good thing to have, unless you have spent a Lot of time razor tuning your engine it will burn more fuel than it uses and the EGR runs part of the exhaust gas back thru the engine, it doesn't harm performance unless something else is wrong.
In short, the evap system is a good one that does not use HP, it also is good for the environment.

Khibbs

I hope it ok if I add on to this thread instead of starting a new one. There is some great info here and hopefully the questions I have for my 81 are relevant and will help someone else who is searching on the same topic.

I'm removing the CCC on my 81 with my current engine swap and have installed a Holley Avenger 670 on top of an RPM Air Gap intake manifold with a new drop base air cleaner assembly.

I certainly want to keep the evap system but I have a few "extra hoses" now that I don't have a connection to the air cleaner and the bowl vent from the carb so I'm looking for some guidance.

I've identified all of the lines from SIXFOOTER's diagram.





1) I've reinstalled the Purge TVS in my new manifold and I've run this line (via the TVS) to the small vac port of the front of the carb.

2) I'm connecting this hose in-line with the PVC valve to the large vac port in the front of the carb

3) Carb bowl vent line that ran to my old QJet

4) To fuel tank. Leaving as is

5) Line that ran to stock air cleaner housing.

My questions comes down to what I do with lines 3 and 5. Can I plug line 3 since I don't have any gas fumes coming from the carb vent and no fitting on my Holley? I'm also hoping I can plug line 5 that ran to the old air cleaner base but I don't know if that needs to used as a vent for the canister. I see a ton of setups were an aftermarket air cleaner is used and they didn't run a hose to a smog fitting the one below.




Any help would be greatly appreciated.

RobertHuggins

One of the fittings on the 1981 charcoal canister is the vent. Marked "AIR CLNR" and routed thru a 3/8" hose to the air cleaner.
Some other models vent through a hole in the bottom of the charcoal canister. Some other models have a foam "filter" built into the top of the charcoal canister itself.

If you still have the stock non-vented gas cap, then your fuel tank needs to vent somewhere.

If you still have the stock fuel pump, fuel is constantly flowing to the engine compartment and some of it is flowing back to the gas tank. This warmer fuel will cause an expansion in your fuel tank. It has to vent somewhere. The original design was to vent it through the charcoal canister. One of the places the charcoal canister is connected to for this venting is the air cleaner through the 3/8" hose.

The connector in your picture is not a "smog" fitting. It is a way to flow air between the charcoal canister and a filtered air source.

The charcoal canister is not neutral on air pressure all the time. Sometimes the gas tank is putting pressure on the canister. Sometimes the purge line is putting a vacuum on the canister.
The slack is made up using the "AIR CLNR" and routed thru a 3/8" hose to the air cleaner.

This is the way I understand this, I hope it helps you.

If you plug up too many of the canister fittings and go for a short drive and remove your gas cap and hear air pressure, then you know you do not have your gas tank properly vented. Please use caution.

Some people give up and just run their gas cap "loose". On this car, it is straight up, so they figure it will not spill much gas. They have given up on controlling the gas fumes when they do this.

Khibbs

Robert,

Thanks so much for your reply. Some great additional info there.

1) What is your take on blocking off the line that is there for the carb bowl vent?

2) If it's easy enough I'm ok with running a 3/8 house to the air cleaner using that fitting. I figured it was for "smog" but most of the use that in the description.

3) I don't have the stock gas cap anymore and although it doesn't state it, I'm pretty sure this is a vented cap based on the holes in the center and then on the exterior rim.



Either way if it's better to have a vent for the canister to the A/C I'm willing to add the extra hose to my nice new setup.

RobertHuggins

I am going to be real humble here and admit up front that there are so many things that I do not know about the charcoal canister, emissions, carb venting, PCV venting, etc.

I think part of the "smog" ambiguity is that back in the 1960's cars did not have PCV valves and they vented the crankcase to the environment. So adding a PCV valve was an early "smog" component. Many 1970's cars have a hose/pipe straight from PCV in one of the valve covers to the air cleaner. Thus the 3/8" hose fitting option for many aftermarket air cleaners could be called a "smog" fitting. For the 1981 Corvette, the PCV vents to the charcoal canister and then the charcoal canister vents to the air cleaner.

Your "vented" gas cap might vent in both directions or it might only allow air into the gas tank to prevent an enormous vacuum as you burn fuel. You can rig up a test jig with an air hose and a mighty vac to test the venting.

Some would say that if you are not going to keep your car stock then use a fully vented gas cap, vent the PCV to the air cleaner, and scrap the charcoal canister. This is 1970 era "smog" control.

1970 cars had fuel pumps that sucked fuel from the gas tank and did not have a return line back to the gas tank.

Some would say that with a 1981 Corvette, the fuel pump was different with a return line back to the gas tank and the gas tank was different with a vent line going to the charcoal canister so you have the potential to do gas fume / emissions control better than the 1970 level.

I thought most old carbs vented the carb bowl inside the air cleaner. Maybe the addition of a hose to vent the carb bowl to the charcoal canister was a 1981 improvement to the earlier design. I suspect you will smell less fumes if you vent the carb bowl to the charcoal canister; but I would like to again state that I am not an expert.