Should a WUR hold vacuum with zero leakage?

[Jay Laifman]

When I hook up a vacuum pump to the 1975 009 WUR, and pump up the vacuum, it slowly leaks out. I’m assuming this is wrong. But can someone confirm?

In thinking it is wrong, I made sure the large o-ring that seals the base was good and the small o-ring that seals the electrical connector was good, and used some Permatex on each. Didn’t change anything.

So that leaves:
(1) something around the diaphragm. I believe the images show an o-ring in there. But, I’ve been afraid to damage the diaphragm and there certainly is no gas leaking there.
(2) Through the atmosphere valve on the bottom of the WUR. I’ve tried to plug it to see if it stops the leak. It hasn’t really. But my plug may not be good enough. If that is bad, I can’t remotely see how to do anything about it. Other than spray it with carb cleaner and hope it cleans out some speck that is blocking the valve from fully closing.

Thanks for any help.

[Jay Laifman]

Never mind. Found the leak. I put it in a pot of water and blew through the vacuum port. Bubbles out the top where that diaphragm is.

[Jay Laifman]

I just sealed up the parts of the top I though were showing bubbles. Didn't change the vacuum leak.

I'm now back to suspecting the bottom atmosphere port, assuming there is a valve in there and that it might not leak when getting pressure, but leaks when it has vacuum.

But this is just a guess. I don't know if there is a valve in there - and if there is, it sure looks like I can't do anything to it other than blow carb cleaner in there.

[Jay Laifman]

Now it is holding vacuum. And the worst thing is I'm not sure what I did that changed it! I did and redid some parts of it - and basically gave up. When I put it all back together, pow, it's holding vacuum. And better yet, the WUR is operating to spec.

One interesting point, when I did the fuel pressure test two weeks ago without having the vacuum hooked up, cold, it came back at .5 bar. Some guides say that is correct (the Troubleshooting guide). Some guides say 1.5 is correct (factory manual). Of all things, now that I put it back together, it is at 1.4 cold, with no vacuum. Strange.