Overfill limiting valve

[Jamiez]

I'm reinstalling the Vapor Canister that a PO removed.  It looks like they also removed the overfill limiting valve.  Any one know where to get a replacement one?  For a 74 challenger with a 360 4 barrel if that matters.

[dodj]

I don't think they are repopped. Probably need to search ebay, c-list for it. Finding one that is actually functional may be difficult. Called the 'vapor separator'

[Jamiez]

Isn't the vapor separator the piece that mounts at the gas tank? I'm looking for the valve that mounts under the hood between the vapor line and the charcoal vapor canister.

[dodj]

Oh ok. Misunderstood. I didn't realize there was an 'overfill valve'. The vapor separator was the only one I was aware of so I thought that was what you meant.

[burdar]

In 73 the vapor line just runs from the separator to the charcole cansiter.  There's nothing else in the line.  There is a valve in the separator that prevents fuel from backing up into the vapor line.  I assume 74 is the same.

To see if the valve is still working, plug the four vent lines with your fingers.  Suck...then blow on the outlet tube of the separator.  You should be able to hear and feel the valve opening and closing.  If the valve is rusted and not working, you can soak it in EvapoRust.  That should free it up.

[Jamiez]

Odd, the manual for 74 shows there should be a valve in that vapor line at the fender. I'll post the diagram from the manual.  A previous owner completely removed the vapor canister, the fuel vapor line was left  intact from the fender back.  The vapor line itself was blocked off with masking tape (always a sure sign of a quality workmanship!).

I'm assuming that the system got removed during one of the carb/intake switches that did not support the vapor system.  Stock it was a four barrel, at one point it had a 6 pack, now it's back to an aftermarket 4 barrel (and intake).

[burdar]

Yah, post a picture of the manual.  I know 74 has some extra valves and vacume lines on the rad.  Maybe they had something extra for the vapor line too.  I've got some pictures of a low mile 74 Challenger that was totalled quite awhile ago.  I'll see if I have them on this computer.  I know they're on my home computer.

[burdar]

Here are three pictures that I have on Photobucket of a 74 engine compartment. 

[Bullitt-]

Here are three pictures that I have on Photobucket of a 74 engine compartment. 

I don't see the "Big" line that goes to the carb. like my '73s 4-barrel has. 

[burdar]

It doesn't look like there is a center nipple on the 74 canister.  In 73, the third hose would have gone into the side of the 2-barrel carb.  Maybe 74 had a different carb setup too.

EDIT:  Looking at the carb closer...it is different then my 73.  Mine has a white plastic nipple ontop of the bowl that the larger rubber hose connects to.  There isn't a nipple in that location on the 74 carb.

[Bullitt-]

It doesn't look like there is a center nipple on the 74 canister.  In 73, the third hose would have gone into the side of the 2-barrel carb.  Maybe 74 had a different carb setup too.

EDIT:  Looking at the carb closer...it is different then my 73.  Mine has a white plastic nipple ontop of the bowl that the larger rubber hose connects to.  There isn't a nipple in that location on the 74 carb.

I have several later model Thermoquad carburetors that do have the bowl vent for the center line, maybe it's a 2-vs-4/barrel difference.
Of course none of the aftermarket 4/barrels have a bowl vent so it would make no difference, just wanted to note it.

[Jamiez]

There really isn't a good picture of the pieces in the manual, just the drawing of the system:


It clearly lists and overfill valve and a connection to the carb

[burdar]

That's just a generic drawing.  There isn't an extra valve.  The vapor separator has the valve in it.  The drawing even says the bowl vent is only on certain models.  It looks like that was done away with in 74...at lease on the 2-barrel cars. 

You've got more problems if you have liquid fuel up that far.  The separator shouldn't allow liquid fuel into the vapor line.

[burdar]

Here's a pic of a 74 360 car.  Still no extra valve in the line and there are only two nipples on the charcole canister.  The only other place there could be an inline valve is on the frame rail where the main vapor line connects to the smaller vapor line in the engine comp.

  http://image.moparmusclemagazine.com/f/31053723/mopp_0307_03_z+1974_plymouth_barracuda+360_engine.jpg


http://image.moparmusclemagazine.com/f/31053717/mopp_0307_02_z+1974_plymouth_barracuda+carburetor.jpg

[Jamiez]

According to the text, the venting depends on the carb.  Some are vented internally and some are not.  It doesn't appear to be as simple as 2 vs 4 barrel but the manual covers all the carbs across the year, so maybe for the Challenger/Barracuda it breaks down that way. The manual states that if the carb does not support it the plug on the canister should be capped, so the 74 still used a 3 hose canister (Fuel Tank, Carb, Purge)

I see now that according to the manual the overfill valve is only on certain car lines. 
V,L,P,D,C do not have vapor separators at the tank and need a limiting valve near the canister (the valve must be mounted vertically making the fender the best spot for it).
R,W station wagons have the valve mounted at the tank.  Standard R,W the drawing is unclear.
B,J have the 4 hose vapor separator at the tank and do not have a separate valve.