911s -74 airbox

Pboden · 10-20-2017, 06:04 AM

Since I bought a -74 911s project for about 1/2 year ago, I have spent a lot of time and money trying to figure out the reason for the irregular mood of the engine. The idle is surging, it always backfire and everytime I rev the engine, it takes a lifetime until it settles down. Surely I have messed with the air/fuel mixture screw and the idle regulator screw.

I have installed new fuel filters, done new complete rebuild of the fueldistributor, inserted new injectors, new spark plugs and wire.

I suspect there is vacuum leakage somewhere and now I have started to focus on the airbox.

A newbie question -
At the front of the airbox (at the frontwall) there is a tube outlet that is sucking air into the box. On my box, there is no hose connected, so since I have no reference whether there is supposed to be a hose connected, I feel I must pop the question.

Did not find any good picture of the specific area, but you see the parts that comes with a airbox

eastbay · 10-20-2017, 08:07 AM

If you don't have the airbox drain set up you need to plug that hole otherwise you are drawing unfiltered air.
If you have not adjusted the WUR your problem probably lies there.
Check this link
Made an Adjustable WUR- Step by step, got Pics!

75 911s · 75 911s's Garage

^As above. It's an oil overflow drain tube. Oil gets puked into the airbox and down a small drain hole at the back. There should be about an 8inch tube that connects that nipple to the firewall (another nipple) and behind the motor is a plastic resevoir with an air tight one way drip "sock" thingy. It can slow drip oil out, but keep un metered air from entering.

Pboden · 10-20-2017, 10:45 AM

ok, so the open hole (about a inch wide) that is in my intake airbox is definitely wrong...

I hold my hand over the hole, and the engine rev pretty much, so I believe I need to adjust the fuel/air mixture and the idle screw

You wouldn't happen to have a picture or part number of both the hose and the drain resevoir ?

Thanks

Pboden · 10-20-2017, 11:01 AM

Found this picture, and I think this is the drain resevoir you refer to.

75 911s · 75 911s's Garage

This is the thread I made on this

Should give the hose dimensions and or part number in the PET on the Porsche website.

Pboden · 10-20-2017, 12:07 PM

One more question
I expect that the black or red "connector" that comes with a new airbox and connects on the rear of the airbox seems to connect to a hose - or should it just be blocked ?

Thanks

75 911s · 75 911s's Garage

I think that is part of the cold start valve. The bottom is blocked off on the red one, which I believe is the correct one for a 74-so no hose attached. I think the black one might be for later cars that have more things on them like Aux Air Valves.

Are you documenting the removal of the old air box with pics and notes. Will make putting the new box in way easier.

eastbay · 02:11 PM

I have the cold start valve mounted directly to the airbox without the standoff. Works fine.
YMMV

On the airbox drain, I just capped the outlet on the airbox since the drain was long gone on my car. Not sure why you would ever need a drain on a well running engine.

Pboden · 10-22-2017, 08:50 AM

Update:

After blocking the hole at the front of the airbox, the engine is finaly running smooth.
Realy smooth, but only for about 1/2 minute - then it just die. Even if I control the throttle manually.

I suspect the WUR, but I do not know this since I do not that familiar (yet) with this engine. Adjusting the fuel/air mixture screw clockwise seems to make the engine run a little longer.

Please advise.

Thanks

fanaudical · fanaudical's Garage

Couple of requests and questions to help you figure this out (there were numerous different CIS variations and who knows if you have what's original to your car):

- Please take a couple of pictures of your CIS installation and post here.

- Which WUR and fuel distributor do you have installed? (Part numbers, please.)

- Do you have the enrichment valve attached to the throttle?

- What are your current system and control pressures? (You'll need a CIS test gauge to determine this.) These are important - you really can't get things dialed right just with swapping parts.

Pboden · 10-22-2017, 12:58 PM

Here are some photos of the setup.

FD - 0438 100 004

The WUR - 0438 140 008

and I believe this is the cold start valve

Sorry for the quality of the pictures, but its dark here in Norway right now. Hope you "get the picture" nevertheless. I can take some more and better ones tomorrow.

75 911s · 75 911s's Garage

The model number for your WUR appears to be correct for a 74. The problem is, that is not a WUR I have ever seen before. It doesn't look like the ones used on a Porsche. It looks like a rusty WUR off a VW or something. :-/ Maybe someone with a 74 can confirm.

Secondly, your plastic insert on your fuel injector that is partially visible in one of the photos, appears to not be seated far enough down into the air intake housing. The injector sits in that plastic sleeve, and the sleeve sits down below the top of the metal, Then the metal is staked on three sides to hold the sleeve in.

I mention this because maybe air is leaking out of the sleeve there. Try some soapy water on it.

fanaudical · fanaudical's Garage

Agreed - WUR looks funny and that injector sleeve isn't inserted quite correctly. What's the tube-like thing sticking off the cold-start valve?

Am still interested in getting values on system pressure and warm/cold control pressures.

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by Pboden

The WUR - 0438 140 008

Pboden,

That is the correct WUR for your '74 CIS. Unfortunately, that is almost impossible to rebuild and difficult to calibrate.

Tony

timmy2 · timmy2's Garage

Tony,
I have your clips for your son's car.
Sent you an email.

Pboden · 10-23-2017, 10:26 PM

Quote:

Originally Posted by boyt911sc

Pboden,

That is the correct WUR for your '74 CIS. Unfortunately, that is almost impossible to rebuild and difficult to calibrate.

Tony

Do you know if there are alternatives WUR for my -74 - if it comes to that I have to acquire one. I believe there are 3 different warm up regulators which do not have vacuum: 911.606.103.00, 911.110.927.00, and 911.606.103.01.

Maybe they can be used ?

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by Pboden

Do you know if there are alternatives WUR for my -74 - if it comes to that I have to acquire one. I believe there are 3 different warm up regulators which do not have vacuum: 911.606.103.00, 911.110.927.00, and 911.606.103.01.

Maybe they can be used ?

Phoden,

Unless you are in "concourse restoration", upgrading to later CIS system version would be a prudent course of action. You have to make a decision in keeping it in stock configuration or to a modified version. First step is to get rid of the TPR (throttle pressure regulator) and replace the WUR-008 with a vacuum assisted WUR. Your '74 CIS does not have AAR, something to consider too. BTW, I am about to mail an adaptor and the fuel line to a PP member doing this conversion right now.

Tony

Pboden · 10-24-2017, 10:21 AM

Quote:

Originally Posted by boyt911sc

Phoden,

Unless you are in "concourse restoration", upgrading to later CIS system version would be a prudent course of action. You have to make a decision in keeping it in stock configuration or to a modified version. First step is to get rid of the TPR (throttle pressure regulator) and replace the WUR-008 with a vacuum assisted WUR. Your '74 CIS does not have AAR, something to consider too. BTW, I am about to mail an adaptor and the fuel line to a PP member doing this conversion right now.

Tony

Sure would like to look more into a CIS conversion if can't figure this one out. Stock is preferred - but if I can't bring it home - I need to look into alternatives.
Tony - u talk about an adapter. Adapter for what?
Which parts would I be needing for a conversion and what can still be used?

Thanks