Should a CIS 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.


By the way, this is for my 1973.5 911T with CIS. The factory correct WURs have not been available or rebuildable for a long time. I have had a 1975 WUR that has a vacuum port. I've had it plugged for years, and running nicely. But, I've been told it will run even better if I can implement the vacuum part too. So I've been trying to get that running now and have found it won't work well with the vacuum hooked up - and that it has a slow vacuum leak.

[Jay Laifman]

Never mind. I put it in a bucket of water, while blowing it in. Found the leak. Through the diaphragm.

[edmayo]

The 73 1/2 has a throttle valve compensator which richens the the mixture at idle and full throttle through mechanical lowering of the fuel by-passed at the throttle valve. A vacuum operated warm up regulator might be over kill.

[Jay Laifman]

Hi Ed,

The throttle position sensor was disconnected years ago when the 009 was installed. My recollection is that that was what people did when they couldn't get 001s anymore.

I spoke with Larry from CIS Flowtech. He said that the car should run better with the 009 hooked up to vacuum - and better than a 129 with the TPS.

Admittedly, I just pulled apart the WUR again and sealed the two areas I thought might be leaking vacuum and it didn't help. I'm now going back to the bottom atmosphere port.

[Jay Laifman]

FYI:

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.

[Jay Laifman]

Here is an update for any 73.5 CIS T owners out there who may end up in this situation. As mentioned, the 129 may be the easiest and most direct replacement. I had a leaky 009 on mine. I had it rebuilt by Larry at CIS Flowtech. I had poor running when I hooked up the vacuum to the top of the Deceleration Valve. I ultimately hooked it up to the hose that goes out the bottom of the Deceleration Valve. This is apparently how the factory did it in 1975 with the early 009 installation. That took away all the running issues.

But then I got a new issue - I found I was having a very hard time starting at warm. My guess was that it was because with the 009 WUR at start, there is NO vacuum, and the pressure goes way down, meaning the car gets richer (once it is running of course, it has vacuum and leans out for all situations other that starting). The stock 73.5 CIS set up would not be that rich. Then the car has the Cold Start Valve pumping more gas in, and compounding the richness problem. I researched how the 911s with the 009 were set up. I found, they came with a "thermal-time switch" which turns OFF the Cold Start Valve when the car gets to a certain temp. That seems like the cure to the problem I thought I was having and supported my analysis of what might be wrong. So as a test, I disconnected my Cold Start Valve micro switch. I've had ZERO problems starting since doing it - warm or cold.

So I'm going to live with it now for a while as is - and see if I ever have any issues. Since I upgraded to the oil fed chain tensioners, my car already has the factory mounting location for the thermal-time switch, and the wiring is easy enough to add. So, if I have any issues with "real" cold starts, I'll simply add it.

Thanks for listening. I hope if anyone has these issues in the future, they will come this way and learn from this.