Anyone with a stock 1975 911 with CIS?

[Jay Laifman]

I'd like to know how one of the hoses on your WUR attaches. There are two plastic pipes, one of which goes to the center of the fuel distributor. One of which might have a banjo that goes to the fuel return. But then there is another hose further down on the body. This should be a vacuum hose that I believe goes to the top hose of your deceleration valve.

If you have a car like this (or otherwise know) I'd appreciate the details on this hose.

If you have a WUR that has a hose going out the base of the WUR, for a total of four hoses, I'm not interested in that one. Just the WUR that has three hoses. As best I can tell, this is a 1975 MY only set up - give or take a few months.

Thanks!

Jay

[gshiwota]

I'm not sure if this helps. Here's a photo of my WUR on my '75 as well as the shot of where the small vacuum line attaches.

[Jay Laifman]

Awesome! That's exactly the hose I'm talking about. Now can you tell me where that rubber hose goes to? Not the plastic one that goes to the fuel distributor. Not the one with the banjo fitting. But the rubber one with the squeeze clamp on it.

Thank you thank you thank you!

[Jay Laifman]

I am told that it goes to a T at the top of the deceleration valve. Here is a picture of a deceleration valve from my year (73.5):
http://forums.pelicanparts.com/uploads18/decel+valve1282590978.jpg

FYI, this is because I have a WUR like yours on my 73.5 because the 73.5 ones are NLA and not rebuildable. But I've never had that vacuum hooked up - just capped. I've always felt my car was not quite as good as it used to be. And I was just told that this is probably the reason. So, I'm trying to see how and where the factory hooked up that hose.

[gshiwota]

On mine that hose is tee'd to the bottom of the decel valve. It's kinda hard to see in this pic but it's connected to a T which is connected to the bottom of the valve. That little off-white gap is the T connector in the picture. The hose at the top of the decel valve connects to the throttle body.

[Jay Laifman]

Perfect! That's exactly what I wanted to see. You've been an awesome help!

[pors1968]

I did 73.5 and 74 .I did a search on forums part for sale. Search for 2.7 a lot good pict engine with cis.

[Jay Laifman]

Thanks. To be fair, I spent all afternoon scanning for pictures. I never could get one that showed what was going on there, or if it did, I couldn't tell for sure what year. So all the more reason I appreciate that Gabe was willing to go the extra step and even take the pictures.

My 911 of 26 years now will definitely be happy about this.

[pors1968]

Nice car pm me if you want pict 73.5 CIS

[gshiwota]

Jay - NP, I'm glad to help. I've been on the receiving end of help on this forum more times that I can remember so it's nice to finally be able to help someone out. It's also convenient that I have a partly disassembled '75 in my garage right now.

This is the best site on the entire internet!

[fanaudical]

I have a '75 S and the 009 WUR. For an alternate perspective, see post #24 in this thread:

Sorry - Yet another CIS troubleshooting thread...

The line exiting to the right side of the photo is connecting to the port on the top of the WUR. I think I have more photos if you need them.

[Hil911]

The biggest difference between the top and the bottom of the decel valve is that the top vacuum is more stable: diaphragms may go up and down but it never draws air. The bottom line (if attached on the vacuum side and not the air side) will only pull hard vacuum until the vacuum at the top opens the valve. Then air rushes through.

As the WUR doesn't do a lot on deceleration, perhaps this doesn't matter?

Oh yeh - nice car! I'm green with envy.

[Hil911]

I was pondering this in the shower. The point of the vacuum in the WUR is that when you floor the pedal, the vacuum drops (pressure rises) and the mixture then needs to be made richer - like an accelerator pump.

If the WUR is fed from the decel valve, then when the valve opens and the pressure in that line increases as air is fed through, bypassing the throttle, that the mixture will then tend to be made richer.

Is that a desirable characteristic?

[Jay Laifman]

I thought when you floor it, vacuum increases - i.e., there is greater suction or pull from the cylinder, which sucks in air from anywhere it can. Thus there would be less pressure.

Oh, and isn't this post the throttle? (I read somewhere that it was supposed to be post the throttle or that it was moved there at some point)

[fanaudical]

Vacuum decreases with throttle opening. (Manifold pressure increases with throttle opening.)

The pressure reference port on the WUR is supposed to connect after the throttle.

The decel valve is mostly opening when you're into a closed-throttle-but-revved-up situation. The air flow sensor/fuel distributor is mostly closing off fuel at that point and so minor enrichment won't hurt.

[Jay Laifman]

Well, I wasn't pondering it in the shower, but . . .

I was looking at pictures. One of there reasons I liked hooking it up to the hose below the decel valve is that the port on the top of the WUR is pretty big, and looks like it would match with the size of the hose below the decal valve. But in looking at a picture today, I realized that even though the OD of the port on the WUR is larger, the ID of the hole inside looks to be about the same, if not exactly the same, as the ID of the hose on the top of the decel valve.

So, if Hil911 is correct that the vacuum on top is better - and I believe he has some pretty good backing behind him since the factory went to pulling vacuum from the top in the later years - I'm now thinking that I might do that instead, assuming I can get some sort of step-down piece for the hoses to fit the larger WUR OD.

Jay

[boyt911sc]

Originally Posted by Hil911

The biggest difference between the top and the bottom of the decel valve is that the top vacuum is more stable: diaphragms may go up and down but it never draws air. The bottom line (if attached on the vacuum side and not the air side) will only pull hard vacuum until the vacuum at the top opens the valve. Then air rushes through.

As the WUR doesn't do a lot on deceleration, perhaps this doesn't matter?

Oh yeh - nice car! I'm green with envy.

Hil911,

The WUR is a control fuel pressure regulator and never been part of the deceleration process. What did you mean by 'As the WUR doesn't do a lot on deceleration'? I've done a lot of testing and evaluation on Bosch WUR 0-438-140-xxx and never heard or encountered a WUR to be involved in any deceleration process. Could you elaborate on this matter? Thanks.

Tony

[Hil911]

Doesn't do "a lot" on deceleration might be nothing! In fact I suppose that it was a deliberate understatement -it probably does nothing because even if it does alter the control pressure, the engine is not producing a positive force.

However we know that at minimum manifold vacuum (lower RPM and pedal to the metal) that the mixture gets richer, so on pullback with a high manifold vacuum I would expect it to make the mixture leaner, if it is not already as lean as it can get.

I had wondered about the purpose of the decel valve - as it is designed (so I read somewhere) to produce a combustible mixture on pullback. Later systems (e.g. Motronic) go further and kill combustion completely (I believe). It is hard to see a way to make CIS do the same. But as lean mixtures tend to cause backfiring, perhaps my suggestion that the mixture goes too lean under high vacuum IS correct and so they reduce the vacuum by adding air.

Hil

[Hil911]

When I think about it, there is the same issue on the mechanical injection - my user manual said to lift the foot completely to activate the microswitch and prevent backfiring on pullback.

But please don't think that I am setting myself up as an expert on cis. I am a scientist and
like to think about why things work rather than just how they are put together, but that is as far as it goes!

Hil

[Jay Laifman]

I installed it over the weekend to the top hose to the DV. Per another thread, I found that my lean/rich adjustment was about 3/4 of a turn from one end to the other. I set mine about in the middle and found it would kind of flutter at partial throttle. I made it about 1/8 more rich and it seemed to smooth it out. But I haven't driven it quite enough to know for sure. I can't say yet if I notice any difference through the ranges yet. I hate to say it. It seems about the same!

But, I also haven't tested the pressures yet with a vacuum hooked up to see how the WUR behaves.