I can't image that the intake track is going to create much more vacuum than that.

Disappointing the valve doesn't close under those vacuum conditions. Maybe shoot some PB blaster into it while under vacuum? If you can see the spring try to pry it gently to see if you can get it unstuck?

On second look, there is a spring under the valve (the 4 little circles). So the default position is "failed close". Intake vacuum creates low pressure on the under side of the diaphragm pulling it down and opening the valve. So it shouldn't pass air with no vacuum. Use a flashlight and look through the valve and see if you can determine the valve position

The anti-backfire valve is supposed to be closed tight shut when there is no vacuum on the control signal port. If you apply enough vacuum to the small control port, the valve should open and pass air between the two large hose connections. And the control port should hold vacuum and not leak down, but I have seen them function "well enough" even with a small leak in the control cavity.

Bottom line... It sounds to me that you unfortunately have two failed AB valves there. Neither of them are any good.  

Thank you both looks like it's back to the junk pile for a third if I can't get this one to unstuck. Now that I think of it when I received it it still had hoses attached and when I took the old hoses off there was a piece of electrical tape covering the secondary Airport where air would enter under vacuum I thought maybe somebody did that just for shipping but it seems now that they realized it was stuck open and had taped shut the secondary port to prevent full-time air coming into or through the valve which probably was creating a full-time lean air condition hard to deal with.

12 hours ago, Richie G said:

there was a piece of electrical tape covering the secondary Airport where air would enter under vacuum I thought maybe somebody did that just for shipping but it seems now that they realized it was stuck open

Haha!! Unfortunately, that's probably exactly what happened!  

I have a couple. Will test what shape they are in.

@zKars I really appreciate that but I do have one more that should be showing up today that I will check first.

And the more I think about my original one being broken makes sense because under certain conditions I did find soot coming out the back of my muffler so wouldn't that also lend to the story of my original valve being broken since I couldn't get any air through it at all to lean out the mixture when required?

Edited July 12, 2024Jul 12 by Richie G
fix word

Of the two, only one works. And it looks pretty much new. It's here if you need it. 

 

Thanks!!! Should know by tomorrow, will let you know.

Saga continues but maybe I have a good one, need someone to weigh in.  This 3rd one i received today is "closed" when i attempt to blow air through it at rest.  i think that's a good start (except it tastes terrible lol).  Connecting the vacuum control port initially i have no pressure held, but, if i close off the smaller pipe like this it will hold pressure.

  Closing the larger pipe does not hold pressure BTW.  As soon as i lift my finger from the smaller pipe it release pressure slowly.  This unit looks just like yours @zKars which the seller mentioned came from a good working 260z.  One thing i do notice which doesnt seem to matter is the control port seems to have been moved to the opposite side which just means i route my rubber slightly differently unless im missing something there.  New one on the left BTW which "aims" the control port towards the engine block rather than on the air filter side.

@zKars does this seem to operate correctly like yours?  it looks super clean down the barrel just like yours does.  If you feel otherwise I'd humbly accept yours and you can DM me for details.

Nope, that ones got a hole in the diaphragm. When you block the upper port you make it part of the vacuum chamber

Unless Zkars says different

Edited July 13, 2024Jul 13 by Patcon

Well that seems like shrike three