Terrordome

Ok. This is a fuel question. A while back I posted about a mysterious spot under the car when I moved it from it's parking space. I made mention of the fact the it was "oily" to the touch and smelled like fuel. A couple of you posted back and told me what to look for, and the culprit was a worn out oil pan gasket.....but that did not take care of the fuel smell.

Fast forward 3 months later and the weather in MD has been 60-70 degrees. Last Friday I had enough of her (The Vette) being in storage and took her out. She ran beautifully and didn't miss a gear. As soon as I pulled in ( after about 45 minutes) and shut her off I noticed and found the source of the fuel smell......I was leaking fuel. Now after I calmed down and got a rag to soak the fuel I realized the leak was coming not for the fuel lines which are on the passenger side, this was on the drivers side located between the drivers front tire and the drivers door. I know the Vapor cannister and Vapor lines are ther, but is it possibile for raw fuel to travel down this line? I hope someone......ANYONE out there has had this happen to them and they are able to tell me, or at least point me in the right direction of how to go about fixing this.

Glenn

Edit/ My car is a 74 BB454 with the original QJet Carb

lucky76

Hook the vacuum line back up from the cannister to your intake manifold.

Terrordome

You lost me? Why would this be the source of the wicked drip

lucky76

Mine was disconnected when I got the car two years ago and I could always smell gas really bad when I parked in the garage after driving it. I read on this forum about the cannister and mine was disconnected. After connecting it back to the intake manifold the smell went away. As for raw gas, maybe pessure on the tank is pushing it out the cannister. There's a rubber hose about 6 inches long from the return line to the cannister, maybe it's broken. This thing is hard to get to.

SIXFOOTER

Also make sure your not overfilling the tank and that the vented fuel cap is venting. Fuel expansion in combination wiith the vac line being disconnected might have filled up the canister. you need to empty the canister.

Glutton4punishment

the problem may be due to an overfilled fuel tank, as the tank (fuel inside) gets hotter, the fuel expands and can travel down the vacuum line. If your vacuum hoses to the manifold are not installed correctly, it may also not be venting the vapour canister, removing the fuel vapour. This can also build up over time, giving you the petrol/gas smell.

bobs77vet

i wonder if the gas vaporizes under heat and pressure and then "condenses" back into a liquid in an environment that is not vented? so i agree hook up the vacuum lines

Terrordome

Thanks guys so much for your input. I was going crazy trying to figure out what it could be. I also read a post by Carl70 and I think I know what to do. Appreciate it.

jotto

I have the exact same problem of real strong petrol smell when parked after a run....when I posted about this, dont think anyone picked up the cannister may be disconnected....guess what Im gonna check!

If the cannister is disconnected, to what point do I reconnect it? My Vette has had a carb change in the past and a few lines were plugged and not connected ( choke etc...not a problem ) Anyone got a good pic?

TIA and sorry to hijack thread...will post seperately if needed...

Glenn, did hooking up the pipe cure your problem?

Terrordome

jotto, mine is not so much the smell.....but actually seeing fuel come out. It wasn't much, so Bobs77 idea of the vapors somehow condensing back into liquid and leaking out makes sense. I amnot one to play around with fuel.....so a call to Tony's Corvettes in Gaithersburg MD may be in order. But first I am going to check out this cannister and rubber fuel lines to see if I can't fix the problem myself. I will keep everyone updated.

Glenn

Steve's74

The evaporative emission control system on the '74 was comprised of several pieces. The carbon canister was designed to trap vapors from the fuel tank caused by expansion in the tank (think hot day). The fuel filler cap was sealed on these cars, and the tank had to be vented. Back at the fuel tank was a fuel separator valve that looks like this:



This valve bolted to the top of the tank in between the tank and the steel vapor line to the carbon canister and was connected by two different size rubber hoses. It is essentially a needle and seat designed to prevent fuel from getting out through the carbon canister if someone over filled the tank (or parked the Vette upside down ). If this part is missing or defective, an overfilled tank can spill fuel into the steel line to the carbon canister, causing fuel to drip out of the canister.

The carbon canister was purged of any fuel vapors that it had absorbed by a separate vacuum line attached to the carburetor. I will need to look over my '74 LS-4 later tonight to tell you whether it is connected to a ported or manifold vacuum source. It's been too long and my memory isn't what it used to be. This system costs no horsepower and reduces air pollution, if the carbon in the cannister is still active. Still, many of them are rendered inoperative, or worse. Mine had the rubber line between the cannister and the steel line cut and plugged when I took delivery of the car, and the fuel separator valve was plugged with epoxy! The attitude in the 70's was that anything that smacked of emission contol was bad! bad! bad! I would verify that you have the fuel separator valve in place, and that the purge vacuum line to the carburetor is connected and functioning. The valve, once unavailable new, is available again through independent suppliers (Zip, Corvette Central, etc)

Steve

TedH

If you choose to replace either the evap hoses/fittings OR the vac canister, both/all are avail from Dr Rebuild. That's where I got the set for my '80 when I had a similar problem back around 1999 with rotted/leaking evap hoses and a failed evap canister; problem solved...

http://www.docrebuild.com/dr-r-web/PCV1.PDF

Hef

A couple of years back when I put my stock 79 back on the road after sitting many years, I also noticed a strong gas smell, but no actual liquid gas leak. It turned out to be one of the evap hoses located in the engine compartment on the drivers side that was rotted away.
Hef

jotto

so the tube from the cannister just has to make its way back up to the intake manifold? On a stock 75 manifold anyone tell me where it should go? Have checked my manuals but pics are not very clear.

Terrordome

Steve, I was wondering about this same piece myself.....you are brilliant!!!! I will be placing my order with Corvette America today. I hope this works. I am still going to get under the car this weekend and see for sure if there is anything else that would need. To everyone: I really appreciate it.

Now if I could just find someone in MD with a 454 I could look at?

bobs77vet

i think i vaguely remember something about my memory....oh well can't remember...but anyway i thought Lars said all of the ports on a Q Jet except for one was unported vaccum....so i guess it doesn't matter which unported spot you use. on my speed demon it is hooked up to the unported spot and it works fine.

shafrs3

I had this exact problem, it was the fuel vapor separator.

Steve's74

You know what they say... the memory goes first! or was that the hair? or the belly?

I forgot to look under the hood of my '74 last night to check out exactly where the vacuum line from the carbon canister connects to the carburetor. Too many sports happening last night. The 17 year pitcher (6' 5" lefty) won his high school baseball game last night, and we came home from that victory to watch his good friend Christy Toliver (she played here for her high school career) and the rest of the Maryland ladies dispatch the Duke team on the women's NCAA. By the time it was over, I was too tired to care. But I'll look this evening, and if the old digital camera works, I'll try to take a picture.

Steve

Terrordome

GO TERPS!!!!!
Send pictures if you can. Thanks Steve

Steve's74

$&!#@!

Sorry Glen, when I got home last night, I found that I had to re-enter my password to post anything here. Apparently the forum software changes are ignoring old cookies for saving the password in our browser. And like an idiot, I forgot where I had written it down. So I couldn't post anything.

Anyway, here are a couple photos that might help you understand where the vacuum hose from the carbon canister is attached to the carburetor. It comes up from the canister and is routed with other hoses over the back side of the power brake booster on top of the firewall.





I have to believe that this is a ported vacuum connection, as I can't believe that Chevrolet would have engineered in this large of a vacuum leak at idle. But I could be wrong, and at the moment, I can't fire up the engine to check (the garage is under our bedroom, the Vette has no exhaust, and the cats absolutely freak out with the open headers!). In any event, on our cars, there is only this single hose to purge vapors from the canister. Later models use a different setup entirely with multiple vacuum hoses. Let me know if different pictures would help or if you have any other questions.

Steve