Vette_Newbie1

I am more looking for a sanity check then specific info about the fuel vapor canister.

To start off, I have purchased my first 'vette; a '74 convertible. Due to the year, it does need some love and care put into it.

I do believe it is the fuel vapor canister. It is located drivers side, just rear of the wheel well, and under the windshield fluid and break fluid reservoirs

I was looking under the hood, and noticed a loose hose, not attached to anything. I thought this to be somewhat alarming, though I have been driving it, without any issues.

After, doing my research, searching this forum, and also looking in the assembly instruction manual and shop manual, I gather that the f.v. canister in this year, has only 2 hose attachment points on the top. (see pic 1)

One of these hoses goes to the tank, I believe. (see pic 2) The other, again, is not attached to anything. The assembly manual does state that one hose is a "vent" hose. If this is true, do I need to worry about this being connected, or can I just tie it down, and still vent to atmosphere.

Again, I am looking for some recommendations, and a sanity check to see if I am looking at this right or if I am way off base.

Thank for helping out
Pictures can be viewed under "My Corvette Photos"

VN

7T1vette

I do not have access to the '74 AIM; but, I think there should be [at least] 3 fittings on your fuel vapor canister. One is the vapor return line from the fuel tank. Another is the larger hose connecting the canister to the vapor inlet port at the carb base. This is called the "purge" line. The third line should be a "signal" line which connects a "ported" vacuum fitting on your carb to a vacuum switch fitting on the top of that canister. This assures that the fuel vapor residue won't be sucked into the carb base at an idle condition, causing an uneven idle. The vacuum switch will only be 'turned ON' when the throttle is depressed a bit, so that ported vacuum changes from "0" vacuum to a high vacuum condition.

Later years had 5 or more fitting for other emissions 'trickery'. But, the '70-74 C3's [I think] had 3 fittings.

Vette_Newbie1

I was thinking that there should be 3 fittings also. But, looking at the AIM, they only identify 2. From looking under the hood, it looks like the F.V. canister has been there for awhile. It might even be the original. I don't know for sure. Also, looking through this forum, there have been discussions in the past, relating to this issue, where people only had two lines coming from the top of the canister.

Also, relating back to a point you made, one line should be going to the carb. However, when I purchased the vehicle, there was an Edelbrock carb installed. There was no line going from the F.V. canister up to the carb. I think when the new carb was installed, that particular port was capped. I did look, and I have no open ports.

It may be worth the time to reattach the hose to the carb, but from what I have read in previous posts, it may be a wash in terms of any additional performance.

VN

Capt Ken

You will notice no difference in performance. The canister is an emission reducer. Mine was disconnected when I first bought the car. When the fuel tank was full I would get fuel fumes in the car while driving. Hooked the vacuum back up, no more smells. My 73 has only two inputs that I can see, haven't checked with a mirror though.

7T1vette

If there are only 2 ports, those MUST be for "Fuel Vapor Inlet" (from tank) and a "Vapor Purge" line to the carb base. For '73-74, the vacuum switch port must have been eliminated....meaning that the vapor canister output does not affect the idle condition, and it can be operated at ALL times the engine is running.

For folks with a 'different' carb on their engine, that 'purge' line could be connected to any fitting that connects to the base of the carb (not the body of the carb). If you don't have power brakes, you could connect the 'purge' line to that booster vacuum port on the back end of the carb base, etc.

Paul L

Yes, it has two ports. The purge hose is the one above the PCV hose. It connects to the base of the carb. Left unconnected it will simply discharge fuel fumes to the atmosphere.



The carb port is the one just to the left of the driver's side air screw.

KenSny

AND into your garage everytime you park it. You will smelll gas fumes in an enclosed space. That's why I connected mine.

Vette_Newbie1

I did some research last night and also I have a few questions, sent to Edelbrock, regarding the hose connection to the F.V. canister. Right now, I am leaning toward re-attaching it to the carb. However, I want to get Edelbrock's take on it. Maybe this weekend I will be able to make some progress on it.

I appreciate the help and guidance.

VN

Swamppro

This is why I really like this forum. A simple search found exactly why I had fumes.

DUB

ONE TIP: Often times if the fuel tank was LITERALLY topped off...fuel can sometimes get pulled into the steel vapor line....and either clog...or water can get into it and cause it to split when it freezes...which I have encountered. I just wanted you to be aware of what other problems can occur.

DUB

Swamppro

Thanks DUB. Appreciate it
I put the vacuum line on as directions and so far garage smells 100% better.

DUB

You can not beat 100% better. You would be amazed on how many Corvettes in my shop can stink of fuel..only to find that the vapor system is all messed up.

DUB

Swamppro

Well it's stinking again. May see about ordering a new canister

DUB

BEFORE you buy one...you better check to make sure your hard line is ALL GOOD...because the vapors can be coming from it. Take the time to do a THOROUGH investigation.

DUB

Swamppro

What do you mean by hard line? From the tank?

1974CorvetteJimCr

See the photos of the vapor line on a 1974. Hope this helps.