I'm not a chemical engineer- but I certainly do wonder what they are putting in the gas these days.

When I converted my tank over for fuel injection - thought I had found a great product to do it. I already had a brand new tank so was looking at a retrofit-

Aeromotive Stealth System- just cut a hole - put the unit in- had a baffle/catch pan and aerospace foam that would keep the gas around the pick -up

It was pricey- but they seem to be a quality company--

Easy to install- nice quality components...

HOWEVER- after a stalled project - I was just going to drain the tank- put in new gas and thought I'd be good to go.

WRONG- in less than two years- no additives- the gas ATE and dissolved the "expensive" foam.

I spoke to several techs and one of the engineers and they admitted there was a problem- and would send me new foam.

I said no way- it'll happen again...ended up with a Holley hydramat- that doesn't seem to be susceptible to breaking down in the gas...yet!!

 

Thanks for the heads up. I hope to convert to fuel injection this coming winter and this is something I need to keep in the back of my mind for future reference.

DC

 

do you continue to fill your tank after the pump shuts off as this over fills the tank and could be causing your problem

 

Please read the thread. This has already been discussed. The volume of fuel in the tank is not causing these valves to fail. When a valve fails internally, fuel can slosh into the vent line at fuel levels even below 3/4 of a tank. These valves are check valves and are supposed to stop the flow of fuel into the vent line. It doesn't matter if that fuel gets there by movement of the fuel within the tank or by overfilling. The OEM valves that came with our cars from the factory worked fine and did not fail like these cheap reproduction valves. The OEM valves only began to fail after many many years of service and the plastic starting getting a bit brittle. This is about poor quality reproduction valves and a poor choice by GM engineers of vent line location. As I said before, I don't need a lesson in how to fill up a gas tank.

DC

 

thinking about going this way as well, what do you think the best way of capping off the gas tank?

 

I did some searching for a rubber cap I could clamp on the vent tube but haven't found one that is rated for fuel. I do have a very thick rubber vacuum cap in the correct size that would probably work until I add fuel injection this winter. Not sure that would be a good long term choice as I don't know how fuel resistant the rubber vacuum cap would be. In the end, I'll probably just clamp a bolt into a short piece of fuel hose and then clamp the hose to the vent tube.

DC

 

I put a 16 gal JAZ tank in my 79 pretty much in the same location as the spare tire carrier. The tank that I got was the blank one and I've cut my own internal fuel pump module, and filler holes. Bought a roll-over vent valve to plug the center hole which is in between the filler and fuel pump. I want to run a canister on it, and am looking for an inline vapor/fuel valve that will work. Once I find something that seems to work, I'll post it up here as an alternative.

 

As I mentioned in one of my posts above, I found several possible solutions within the marine industry. The problem was that every device I found was physically too large to mount in a vertical orientation and be above the vent line of the factory tank. You might have better luck with your setup. But, I hope you find something that works. We need a better solution than the piece of junk reproductions currently on the market. I'm in the process of swapping the engine and transmission in my '73. The new engine will be fuel injected so I will also swap to a tank setup for fuel injection that comes with the vent tube located in the top near the center where it belongs. Hopefully I won't need any kind of check valve with this setup.

DC

 

This is the set up used on most new modern competition ski boats.
It was what was on my Malibu and my Mastercraft, and what I will be running on my 73.
Richard454 installed this same unit on his 71 project and you can see it installed in his build thread.
Simple and fits at the rear of the car at the fuel tank.

 

Hey, did you happen to settle on a tank / fuel system venting solution yet? I'll be doing this pretty soon to my 71. I also don't want to route the roll-over valve to the antenna location. I thought I had a plan, but then I read about how unreliable the re-manufactured separator valves are. The EFI tank kits out there (i.e. Tanks Inc., Holley, etc.) have the vents built into in-tank pump unit. I used one in my 63 Nova with Fitech, but instead of using the check valve routed high (as they recommend), I used a II Much Fab canister mounted above the tank. This works perfect, but is clearly is not an option on the C3.

My original plan was to use Holley's new "OE Style EFI Fuel Tank Modules" on a stock tank with the factory EEC setup (separator/charcoal canister/etc.). The cool thing about this module is that the in-tank pump self-regulates the pressure at 58psi (so no return line needed -- you have one outlet just like the stock sender). Of course, if the separator valves are garbage, I might need to think of something new. Perhaps just plugging that vent port on the stock tank and using a 63-69 vented cap would do, but I worry about smelling up the house with fumes.

- Jon

 

Hey Jon,

Welcome to the forum.

I settled on a new tank from Tanks Inc. I'm in the middle of an EFI engine/transmission swap at the moment and haven't gotten far enough along to install the new tank. Because this new tank vents near the middle top of the tank, I'm going to just run the vent line direct to the vapor canister without any sort of check valve at first. If I end up getting fuel in the line with that setup, I'll have to figure out plan B.


Another update. Because of the failed separator valves, the vapor canister in my '73 ended up getting completely saturated with gas a few times. I talked to the owner of a hot rod shop and he said anytime a charcoal canister gets saturated with gas, he replaces the canister (or at least the charcoal). I can understand why. While starting work on my engine swap I noticed my existing canister was leaking charcoal on the ground. There is some type of breathable membrane inside the canister that had failed and was allowing charcoal to escape out of the bottom. I ended up dumping all of the charcoal into a pan and it absolutely wreaked of gasoline even though it had been several months since the last saturation. Even after a week in a shallow pan the charcoal still smelled strongly of gasoline. No wonder I could still smell gas in engine bay even though the engine was out.

'73 and older vapor canisters are no longer available but '74 and later model canisters are still being made by AC Delco. I ended up replacing mine with the '74 style. The difference is that GM eliminated the small vacuum hose that goes to a ported vacuum source. So, there are only two connections to make. One to the tank and one to tee into the line to the PCV valve. If you absolutely need the original functionality, AC Delco also makes a stand alone purge valve that could be used in conjunction with the '74+ canisters.

DC

 

Thanks for the welcome!

You'll be happy with the Tanks Inc tank. My recommendation is to use their cork gaskets coated with Permetex Aviation Make a Gasket sealant. Their neoprene gaskets are know fail (or at least they were a couple years back when I was building my Nova).

I just got off the phone with Dan at Vetteworks and might have a Plan B option for ya... It'd be expensive since you've got the new tank already. They sell a tank with the OE Delphi pump used on later models. It regulates pressure at 58psi AND has a vent port, with check valve, built in that can be tied into your existing EEC system.

- Jon

 

I’ve been following this topic in hopes to come across some answers in regards to changing from non vented to vented and eliminating the fuel separator. Is it as simple as plugging the the tank and getting a vented cap? Does a vented cap not only allow air to enter as fuel is used, but also allow pressure to escape such as when it gets hot in the sun? Thanks for any input

 

That's what I ended up doing after numerous failed separator valves. The only problem is that you'll get more gas smell in the garage - especially on hotter days and with a full tank.

DC

 

Was it in 71 or 72 when Corvettes went from a vented fuel cap to a non-vented fuel cap and added the charcoal canister?
I purchased a vented cap for my 73 and plan to run it when I do my resto/mod.
Over the years I've owned numerous cars, boats and motorcycles with vented fuel caps and have never noticed any gas fumes in the garage.

 

DC - - thanks for the very useful info. I too have had multiple failures of this plastic separator valve and am going to a vented cap and will plug the hoses to the separator. Question - is plugging the hoses to the separator the right approach or is there something else I should do ? Thanks in advance.

 

Plugging the hose to the separator and running a vented cap will work. You could just pull the hose off of the tank nipple and put a fuel resistant cap on the nipple with a clamp. I just pulled the hose off the separator, cut it as short as possible, inserted a bolt into the hose and then clamped it.

DC

 

DC - thank you ! Appreciate the response.

 

I decided to get the tanks inc. setup as well. When removing my old tank, I realized my sender had a bad leak, so I thought it'd be best to avoid having a tank with one on the bottom if I could. Anyway, I looked at my rollover valve from tanks inc. and realized the screened cap is threaded on to it. My plan is to remove the screened cap, get a female 1/4-npt to hose barb 90, mount it vertically as high as possible, and plumb it to my vapor canister line. Looks like tanks inc. recommends that as well at the bottom of this article (https://www.onallcylinders.com/2015/...er-vent-valve/)

Hope it works ... hate the fumes!

 

Interesting that you mention doing this. I had the same realization and just finished up mounting the rollover valve this past week.





DC