Two way valve -fuel tank to charcoal canister

[jagonza]

What does the two way valve do ? Mine has been removed, just wondering if I need to replace it.

Goes from fuel tank to charcoal canister

[RRoller123]

It maintains the proper operating pressures for the fuel vapor system. One way pushes displaced fuel vapors from refueling up through the charcoal canister to be burned later, as there is always some air being pulled through the canister when the engine is running.

The other direction allows make up air to be taken back into the fuel tank as it empties during operation. The two way valve makes sure that the pressures needed to regulate the flow are maintained. It is not an expensive item and should be included in the system. Probably could get one from a member here, or they are readily available from the various vendors. Older ones may get gunked up and may stick, but they can be cleaned and tested with a good strong breath through them each way.

They are directional, and if memory serves me correctly, the flange side goes to the gas tank side, so the low pressure restriction allows make up air to flow easily back into the gas tank.

[jagonza]

here is a picture of what i have on a 77-carb'ed. nto like the the samller "UFO" style other have.

mine is in the trunk near the fuel filler.

i am getting vacuum on the tank that overpowers the fuel pump and i "run of of gas" with about half a tank. I assume that either this or the charcoal canister has stopped allowing makeup air into the tank.

No one seems to stock this, i assume that i can replace it with the UFO style.

anyone know how to test this and or the charcoal canister to see if they are allowing makeup air into the tank ??

[RRoller123]

If the unit is plugged, and you don't have a vented gas cap, then there is no other source of make up air to the tank. (That I am aware of in a carbed car?) I should have looked at your sig to see that it was a carbed car, sorry, but I suspect that the operating features of the charcoal system are exactly the same.

So one solution would be to use a vented gas cap, that will supply the gas tank make up air. But the better solution is to either clean the 2-way valve that you have, or replace it. But one caveat:

I tried cleaning mine, and it sort of worked, and I stress sort of, because the cleaning changed the pressure trigger levels, which I am sure would effect the air flows. I was able to get it cleaned out enough that it would pass air both directions, but the new one displayed quite different pressure trigger levels.

Pete

[RRoller123]

sorry, double post, fumble fingers

[jagonza]

What if i remove the valve and just put a straight connector in its place, would that hurt anything ?? I get that it may allow more vapor out but it wouldn't be worse than a vented cap and it would be caught in the charcoal canister ?? right ??

[baltobernie]

The valve you have actually has three ports; the two nipples plus the back of the valve is open. I don't think the later model valve would be equivalent.

I've been chasing this issue for years without success ... replaced all the hoses, refurb'd the canister, replaced the valve with a known-good salvage unit, etc. My "solution" was to drill a 1/8" hole in the gas cap and ignore the fumes in the garage. The valve, BTW, is NLA as you have discovered, and ethanol destroys them quickly.

Sorry I couldn't be more helpful. I have the pages from the factory manual if you want them.

[jagonza]

ok , i replaced the two way valve with just a straight connector - i could blow air through it no problem,

went for a run - ran great for about ten miles of straight easy driving, then i made a sharp u-turn and the stumbling started up and it stalled again.

i opened the gas cap slowly and heard/felt no air going in or out. I don't think it is a vacuum/make up air problem.

I am leaning towards a fuel pump that can't re-prime when it gets an air slug from the tank sloshing to one side. it's a facet cube pump . doesnt seem to make any noise - i have heard people complain about these making noise - mine is pretty quite.

before i put out for a new pump does anyone have any other ideas ??

I refiled the tank and will see if it happens with a full tank. It has only happened at about 1/2 tank before.

[baltobernie]

Have you checked the fuel pickup? If you haven't done so already, remove the sender/pickup assembly from the tank, and look for any irregularities in the pickup tube. Compare it to photos of new units.

I've been able to run my car to a point where the gauge needle no longer moves without incurring stumble, and I have a Facet cube pump too.

[jagonza]

So i ran it with a full tank, took some high speed turns, up hills down hills, no issues at all. hmmmm

also took a look at the pickup tube in the tank and dont see anything - other than the filter sock is dissolved away.

I am leaning towards fuel pump issues. with the car running it showed 13+V at the pump, it doesnt make any noise , but you can feel it pumping if you put your hand on it.

I will check the screen in front to the pulp for build up.

does anyone know if the ADFA carb has a built in filter screen inside the body somewhere ??

[baltobernie]

I am leaning towards fuel pump issues. with the car running it showed 13+V at the pump, it doesn't make any noise , but you can feel it pumping if you put your hand on it.

You're describing normal pump operation.

I will check the screen in front to the pump for build up.

Good idea. Any chance you have restriction between the pump and the carb? Maybe some old rubber line along the route? If you've ever seen the Facet "cube" pumping unrestricted, it is impressive. Not a lot of pressure, but the volume would feed a wide-open V8. If there's no restriction before or after the pump and all the lines are routed correctly, the next step is probably pump replacement.