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Posted by: si2t3m Oct 9 2004, 05:47 AM

I'm seeking advice.

So I played with the gas tank again tonight...

The tank looks much better without the evaporation tank and charcoal canister.

Is there someone out there running without them? How did you deal with the small hose on the filler neck? I took mine for a drive and got a strong fuel odor after a sharp corner. Fuel sloched in the tank and spilled out of the vent line (now attached to nothing.

Is there an alternative or i'm stuck putting back the evaporation tank & charcoal canister?

Posted by: ruddyboys Oct 9 2004, 06:26 AM

You could run the small line to the engine compartment and mount the carcoal canister there.

Posted by: Joe Sharp Old Oct 9 2004, 07:09 AM

Some motorcycles run a check valve in thier vent line.
Joe

Posted by: J P Stein Oct 9 2004, 10:34 AM

I ran a plastic hose from the vent into the big drain hose.....melt a hole (or drill) in the big hose and run the small line down into it about a foot.

Posted by: si2t3m Oct 9 2004, 11:29 AM

I like that check valve idea.

Running to the local flap!

Marc-André

Posted by: dmenche914 Oct 9 2004, 12:17 PM

Modern cars have sealed tanks, that is why they hiss when the cap is opened. Modern cars also have charcaol cans. 914 era cars have vented tanks, however they are vented to the charcoal cans to absorb the fumes, and when the car is running the cans are sucked out by the engine and burned. Burned gas being better than raw gas in the air.

You have a vented sytem, now with no charcoal recovery cans. Your gas tank is not designed to be sealed, so do not plug the vent, else you might pull a vaccum when on a full tank, that might starve the engine under load.

In making a vented sytem, much like the cars had prior to laws requiring charcoal cans you need to consider two things:

1. How to make the vent line minimize the chance of leaking gas out of your tank in a roll over accident, This is a safety issue that is easily accomplished by extending the end of the vent hose to the bottom of the chassis, just above the ground, and secure it so that if tipped upside down, it will stay in place, and thus be higher than the top of the tank. Roll over with a short vent line, and all the gas above it pours out, you die in fire, bad thing. Also this puts the vent down low, away from the car as much as possible, minimizing odors, and might provide a slight road draft effect, allowing a slight vaccum to be maintained in the tank, helping reduce odors from a worn gas cap or such.

2. You should have a trap that will catch gas that may slosh when driven around a corner or leaked when parked on a side slope. This could be done with a loop of line secured near above the tank top, loop the line to run across the tank a bit and then U-turn back to the vent fitting and down towards the ground. This gives a small place for gas to go, yet allows it to drain back to the tank, rather than on the ground once cornering forces are reduced (which can be considerable in the nimble 914)


At any rate, that is the scoop on making an air vented tank. My 1961 VW Bug has just such set up, all stock, that's the way they did it, and that's the reasons why.

Safety, and minimize spillage.

Of course, unless supper light wieght is an issue on a pexiglass windowed, no interior track car, you could leave the charcoal system inplace, it is light, and does not rob any power at the engine, and it does reduce a significant amount or air pollution.

I do not have the exact figures, so I might be way off, but I have heard that the old air vented cars had as much as half or so of the smog caused by the engine, and half from gas fumes leaking out the tank, rather running, or parked, they polluted a great deal because they had air vented gas tanks.

good luck.

Posted by: lapuwali Oct 9 2004, 01:20 PM

The mentioned check valve is there to prevent pulling a vacuum on the tank. A one-way valve so arranged that air can go into the tank, but not out, will prevent fumes from escaping and still allow the tank to be vented. The one thing this doesn't handle is pressurisation caused by heat expanding the fuel in the tank (and raising the pressure of the air above the tank). To handle both cases, plumb the tank vent into catch can vented into the engine's airbox. A charcoal canister is a nice thing to do there, and will be pretty effective at reducing fumes from getting into the air. This canister can be mounted anywhere, and the hoses are there on the 914 to allow it to be mounted in the engine bay easily enough if you want to remove it from above the tank.

Posted by: SirAndy Oct 9 2004, 04:32 PM

yes, i junked the whole assembly ...

take off canister and expansion tank, take the very small hose that went into the expansion tank and shove it *inside* the big plastic hose that goes out the bottom.

take off the 2 hoses that go to the back (engine bay) under the drivers side rockers.

detach one from the air-cleaner and plug the hole.
detach the other from the fan housing and plug the hole.

voila!
Andy