Fill tank, honk horn, die fiery death?

[RallyJon]

Still learning the idiosyncrasies of my 71 911. When I first filled the gas tank, fuel squirted out on the ground from the front of the left front fenderwell. Until it was down below 3/4 tank, I would smell fuel on every hard right turn.

I saw the vent hose under the hood, and when I had it up on a lift today and poked around, I see that the vent hose just terminates in the fender. It's directly above the dual horns there, and I'm a bit concerned about the risk of explosion.

a) Is this the way the tank was vented from the factory? If not, what's the stock arrangement?

b) Why would the tank overflow when I fill it, and continue to spill out of the vent tube while driving? Is there supposed to be some sort of check valve or something?

Thanks, -Jon

[pbs911]

I have never filled my tank past the auto-shut off at the pump, and have never had full overflow from the tank. Don't know if this helps since I am unfamiliar with the overflow set up on the early cars, but spilling out the overflow tube until the tank is 3/4 full is not how it came from the factory!

[katigbr]

Jon,
I had a similar problem after I removed and replaced the tank in my 72. It turns out that I had improperly attached the overflow tube that extends from the filler neck and attaches to a tank in the front fender. This caused fuel to puddle around the filler neck and then escape down the drain at the rear of the fenderwell.

In re-reading your post, it sounds like you don't have the overflow tank. Not sure if all early 911's had this tank perhaps someone on pp can confirm.

Once I hooked everything up I no longer had the fuel spillage problem, even with a full tank at track cornering speeds.

Rcik

[RallyJon]

it sounds like you don't have the overflow tank

That's for sure! I don't see it listed on any of the parts sites. Anyone got a picture of the elusive overflow tank?

I found a few other threads on this topic--but lots of questions and no answers.

[katigbr]

Jon,
You can look at this Pelican Parts - Early 911 Fuel System Diagram to see the overflow tank. The tank is part number 3 and connects to the filler neck by a series of plastic tubing and y-connectors.

Rick

[pwd72s]

And...should you restore this "marv-HELL-ous" system to originality? When you still smell gas in the cockpit after a fill-up? The first place to look is the hose connections on #2 part in the diagram. Isn't it great when government moves in and makes a new mandate, the terms of which are written by bureaucrats? This diagram is but one small example....

[RallyJon]

Good diagram. But what's #2? It seems to be in parallel with #3. I figure that one of those boxes (#2 or #6) is the charcoal canister, right?

But nevermind what was stock. I'm certainly not going to restore a kludgy emissions control system when I really just need a splash control system. The practical question is: what sort of container/ filter/ valve could I put on the end of that hose to prevent fuel from splashing out, while still allowing the tank to relieve pressure differences when filled, as fuel is used, and when the temp changes?

[RallyJon]

Aha! Look what I found:

"Discriminator valves offer the ultimate in fuel venting. This valve shuts off fuel when full, eliminating the need for a catch can. Also offers positive shut-off in case of a rollover."

[Elombard]

Hmm

Let me know how that works, I am ready to rip all that sheist out of there!!! Good god what a cluster, must weigh 20 lbs!!

[pwd72s]

RallyJon? Make all vent hoses higher than the level of the tank filler neck...simple, right? You can find #2 tucked up under the dash, right behind the steering wheel area....a LOT higher than the trap located in the left front wheelwell...#2 is probably the highest point of the entire system. The valves you found? So far, so good...

[RoninLB]

I pulled the gas box contraption out..I took small vent hose going in and looped it a few times/held loop together w/tie wrap..if filling gas tank to very very full, gas will discharge on gas station ground...no smell when driving/no leaks after very full gas tank is only full..........Ron

[ccandgc]

I was poking around under the dash from the trunk side, and I was wondering what that thing was...well now I know. What the he**???Why did they put it up there??


ChadC
71 911S Targa

[Chuck Moreland]

Rallyjon

Where are you getting the discriminator?

ccandgc

I believe it is located due to the height. It is the highest point in the system, so fuel flows aways from it.

[RallyJon]

http://www.racerpartswholesale.com/fsafe9.htm

I'm waiting to hear back if it can be mounted horizontally. I doubt it, but it would make installation easier.

In another direction, my mechanic had a suggestion after looking at the diagram posted above. He says that back before emissions rules, there was such a thing as a vented filler cap. Looking at the diagram, if you ran the tank vent back up to the little fitting on the filler neck, and used a vented cap, it might work. Simple.

Anyone know if pre-emissions 911s used a vented cap, and if so, will it fit the later filler?

[katigbr]

Jon,
In looking at that catalog, I think the part that might work best is the one they labelled 3/8" roll over valve. It is the right diameter to fit the filler neck overflow and would prevent the fuel from spilling while allowing the system to receive fresh air. I think the fresh air access is important to prevent vacuum from building up.

I actually just changed gas tanks and ripped out all of the emissions stuff and have a single 3/8" overflow/vent line at the rear of the filler neck. Currently it drains into a water bottle attached with a barbed fitting. I think the inline "roll over" valve might work and will let me get rid of the water bottle.

This works for us early 911 that are emissions exempt but assume that the system must be retained for new 911s.



Regards,
Rick