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The problem is over time the check ball float sticks because it has sat so long in one position. One can remove the check valve assembly. Once removed you can spray a light lubricant into the valve assembly let is sit for a while. Then shake the assembly the ball should come free and should be good for another 50 years. The reproductions are not very good and fail regularity..
To test the valve, blow air through either port. The valve is open and air should flow freely through both ports when in its normal position as mounted on the tank. When positioned up-side-down as shown, the valve should close and permit no airflow through the ports.
Yes. GM was just 'throwing spaghetti at the walls" to satisfy EPA regulations. All of the U.S. based car manufacturers were in the 'head-stuck-in-the-sand' mode when it came to emissions and [particularly] with fuel mileage. As a result, they got their "lunch eaten" by the Asian car makers in the 1980's {and beyond}.
I'm wondering, as I'm working through the possibilities of this fuel leak....since the system is designed to be pressurized should I be hearing a "swoosh" when I open the gas cap?
I'm wondering, as I'm working through the possibilities of this fuel leak....since the system is designed to be pressurized should I be hearing a "swoosh" when I open the gas cap?
Alan
Is the swoosh sucking in, or blowing out?
The tank is not designed to be pressurized, if everything is working correctly.
The tank is vented released by the EVAP system. The EVAP system allowed fuel vapors to be captured by the charcoal allowing the have the sealed gas cap. Some will point out that 1970's had a sealed cap. Which is true but any 1970 sent to California had the EVAP system installed. Also the tank has an additional release valve on the top of the fuel tank to prevent an over pressure.
I have a 72 LT1. I had very strong gas odor after I would fill it up. I never saw any gas leaking, but a strong raw gas smell.
I removed and then rebuilt my charcoal canister. There was some improvement, but still gas odor. I noticed some stains on
top/side of the left muffler. After some further research, I decided to change the tank vapor valve. The gas odor was solved.
I also replaced all of my rubber hoses and clamps to/from the canister and vapor valve. Everything works now as intended.
I’m wondering what would happen if your 2 lines at the canister from the carb and PCV were reversed and if you also had a
faulty vapor valve? Could the canister pull gas from the tank? Also, are the lines at the vapor valve correct? They are tank to valve
and valve to the metal line that goes to the canister.
Most of the above is easy to check and confirm.
I'm in the same boat with my 71 for a fuel vapor canister, none available although I have found through my searching they can be rebuilt by replacing the charcoal and filters. You mentioned eliminating the canister, I'm wondering if that's also an option, how one would go about it keeping in mind safety and foul fuel smells.
BTW Lars recently rebuilt the carb for my 71 and I couldn't be happier with the results! Big improvement in idling, starting and overall performance. Lars was patient with my many question and the whole process was educational and fun. We are very fortunate to have Lars providing this service, his attention to detail, knowledge and expertise are exceptional. He most certainly ratcheted up the factor for my 71!
No fuel 'storage' system in a vehicle is pressurized. That would be a very dangerous situation. ALL vehicle fuel tanks are vented: some via the cap; some via a vent on the tank; GM's vapor collection chamber has a vent at the bottom and as a drain (if necessary) in event of a system failure.
What I originally perceived as a fuel leak is actually the vent in the bottom of the canister. My concern is the volume of gas that will purge out of it at times. A pint of gasoline spilling out onto the garage floor can be disturbing let alone the wifes comments about the smell. I replaced the gas cap yesterday and am experimenting with different fuel levels when filling the tank.
In the end I think its going to take replacement of the fuel separator but I'm tackling the easy things first.
I'm in the same boat with my 71 for a fuel vapor canister, none available although I have found through my searching they can be rebuilt by replacing the charcoal and filters. You mentioned eliminating the canister, I'm wondering if that's also an option, how one would go about it keeping in mind safety and foul fuel smells.
BTW Lars recently rebuilt the carb for my 71 and I couldn't be happier with the results! Big improvement in idling, starting and overall performance. Lars was patient with my many question and the whole process was educational and fun. We are very fortunate to have Lars providing this service, his attention to detail, knowledge and expertise are exceptional. He most certainly ratcheted up the factor for my 71!
Alan
Alan
I eliminated the Transmission Controlled Spark (TCS) system on my 73 not the Evaporative Emission Control (EEC) system. Not sure I would want to go there, I think it's easier just to repair or replace that system and keep it operational.
What I had been referring to in previous post as the EVAC system is actually the EVAP system. In short, for a 1971 Corvette an early emissions control that collects fuel vapors in the gas tank by way of a fuel separator valve, the vapors are fed to and collected in a charcoal filled canister located behind the vent in the driver’s side fender. When the engine is running and the vacuum reaches a certain level the vapors are released from the charcoal and burned in the carb. Fascinating system!
The charcoal canister has a drain in the bottom to allow gasoline to purge.
My issue is when the tank is filled over ¾ full (2” below the filler neck) gasoline will travel to and collect in the canister. After the car has been driven for an hour and shut off a pint of gas will drain out onto the garage floor. Not a great sight to witness!
I suspect a fuel separator valve at the top of the tank is bad. Requires removal of the tank to replace. The fuel separator valve is basically cheap plastic and the failure rate is high including new replacement valves.
The charcoal/ filtered canister is not available as a replacement but can be rebuilt and replenished.
I have traced and verified to the best of my ability that all vapor lines are intact and there are no vacuum or vapor leaks.
I’ve changed out the gas cap but no difference.
My plan is to at some point pull the gas tank, replace the valve and rebuild the canister. Until then I fill the tank ¾ or less.
Before executing this plan, I would greatly appreciate any impute from fellow forum members whom have already been a great source of knowledge and help along the way.
The charcoal/ filtered canister is not available as a replacement but can be rebuilt and replenished.
Alan
Hey Alan,
Just a heads up but if all you want is original functionality and don't need original parts, I believe you can use the '74 and up charcoal canister with an AC Delco purge valve. See post #5 in this thread: https://www.corvetteforum.com/forums...lier-cars.html
I was able to change my fuel separator valve without dropping the tank or the muffler but it was basically a one handed blind operation. I was able to barely see the valve from one angle but could not see it once I put my arm in the space. I used my cell phone to take some photos and video so I would be familiar with what I was doing. One thing I did the second to last time I replaced the valve was to flip the bolts around on the bracket so that they become studs with nuts. That made it a lot easier to put the new valve in place as it could hang on the studs until I could fetch and install the nuts. I had to bend the bracket slightly to get one of the bolts to become a stud but I was then able to bend it back.
As I mentioned in my post 28 above...I replaced my vapor valve without dropping the tank also.
I did remove the muffler for easier access because I also replaced the rubber lines and spring clamps
at the same time. Worth the several hour investment to rebuild the canister and replace the valve and
ultimately eliminate the gas odors.
factor for my 71!
