beg3yrs

Hanging out in another Z forum (I know, flame me) someone mentioned there is supposed to be a flow restrictor in the vapor line between the vapor recovery tank and the charcoal canister.

Searching through two FSMs (1974 260 and 1975 280) I could find no mention of this dastardly little device. I did find it in the Haynes manual though it's mentioned almost in passing and the diagram shows it but there's no call-out.

I think its function is to let fuel vapors flow slowly into the charcoal canister from the vapor recovery tank when the motor is off and then be a restriction when the motor is running and there's plenty of vacuum. If it isn't in place, too much vapor from the recovery tank gets vented directly into the front intake manifold port and the air/fuel mixture gets messed up.

I'm thinking since I don't have this installed, it's one of the contributing sources of my motor doing odd things such as surging and insisting on running only rich (this is on my list to address but not yet at the top).

Parts stores in the area have no idea where to get something like this.

I'm playing around with cobbling together something using some stainless tubing of various diameters but I'm kind of flying blind as I don't really know how big the orifices should be on either side nor how long it should be.

Anyone know more???

beg3yrs

Here's the diagram from the Haynes manual. The restrictor is shown at the very top in the circle. As you can see, it isn't called out. There's a short discussion on the previous page which I summarized in my previous post.

Skully

Step #4, could be the orifice?!
IZCC Club Organization:

I know its super **** quality, but page 32 says that it draws vapors from tank through the ORIFICE.
http://www.spooledupracing.com/downl...l%20System.pdf

"Under normal driving condition, a large amount of air is sucked into the canister. An orifice provided in the vapor line on the front of the carbon canister, prevents excessive evaporative fuel from being sucked into the carburetor, and prevents an erroneous engine operation."

As far as how length, it should not matter. So if you even put half inch long 1.5 mm restriction in it, it will only flow for that 1.5mm opening. Length should not be a concerning factor here, as friction is not the issue at matter. If that makes sense?

Heres more
Page 15
http://www.mikesrealm.us/FTP/70-73-2...n%20Manual.pdf

beg3yrs

Hi Skully, thanks for being a great detective.

First of all you found a reference to the orifice in the FSM, I was looking in a different spot that also referenced the canister but did not speak to the orifice.

Then, you found two references to a flow restrictor internal to the "flow guide valve". Seems this valve is used in an earlier configuration of the vapor recovery system which did not utilize a charcoal canister but ... AFAIK, it's the only piece of documentation that actually mentions a diameter. Even though it's for an earlier version of the system, it's the best shot at what was used in the next version so I'm going with it.

Seems 1.5mm is pretty close to one sixteenth of an inch for us metrically challenged folk here in the US. Best of all, one of the pieces of steel tubing I've got has an I.D. just that size.

I'll see if I can fab this up in the next few days and will post results.

Thanks! I know you spent some time doing the search and it's really appreciated.

beg3yrs

Built my own flow restrictor with some simple parts.

1) A 1/4" brass tubing mender
2) A piece of specialty tubing from the local hardware store. It's aluminum (or is that aluminium?) with a 3/16" O.D. and a 1/16" I.D.

Had to drill the tubing mender using a 3/16" bit as it was a tiny bit too narrow to accept the aluminum tubing. I only drilled about half an inch.



Then it was a real simple process to cut 1/4" of the aluminum tube using a Dremel tool and tap the piece into the mender. It was a pretty tight fit an I'll mount that side toward the vapor recovery tank so suction will act to retain the part in the mender as well.

Sorry about the focus.


Now, if only I could get the car back from the A/C shop, I could install the part and see if the motor runs any better ...