Quick Vacuum Line Question

[NoYouRelax]

I am in the process of reinstalling the CIS system and making every fuel and vacuum line firm and tight. It was very sloppy loose coming apart and old hoses were suspect...RTV and sealant everywhere.

I found a vacuum source, and have yet to find a mating hose for it. It's a connection about 3/8" on the bottom of the airbox. It should be a major vacuum source.....see the yellow arrow in the picture. Any idea what should be connected here?

[1982911SCTarga]

That's a mold sprue or something similar for the airbox. It's blocked and thus not a source for vacuum.

What does the writing say on your engine tin, "Jack Middle"?

Brian

[NoYouRelax]

Thanks Brian. I am certain the "mold sprue" is open to the outside, but will double check. Writing says "back middle" my markings as I disassmbled things.

Bill

[NoYouRelax]

I double checked it and it is definitely a port. The closest match I could find in terms of hose size and proximity is from the cruise control unit.

[timmy2]

Hard to tell orientation on my phone, but it looks like the drain for the airbox on the filter side. No vacuum source there. Pull the filter and you will see it.

[NoYouRelax]

Drain makes sense as it is at the low point and upstream of real vacuum. Hard to believe it would be so open to the atmosphere on the clean side of the filter though.

[Brown747]

I believe there is a rubber plug over the outlet on the inside of the airbox. Pull the filter and have a look.
HTH

[E Sully]

I'm not sure what year you have, but on mine it is a drain for oil that collects in the air box from the oil tank breather. A section of hose connects to it that goes to a cylinder with a rubber valve on the end. It goes out by the flywheel. There are a few posts on it, I will see if I can find one.

[E Sully]

Originally Posted by E Sully

A few years back I had a small leak in an air box I got when I picked up a complete system for spare parts. I removed all the screws and carefuly pried open the seam with a small putty knife, and then sealed it with a glue I found in the hardware store that claimed it was fuel and heat resistent. I can't remember what it was now, but next time I'm out I will see if I can locate it.
In case your interested, here are pictures I found, first being a 74, second a 77. Seems the drains were still in use. Parts you found must be a different system.
Part 11 in the diagram is 911 108 021 02
Pelican Parts - Product Information: OEM-91110802102
Part 12 in the diagram is 253 260 180
Pelican Parts - Product Information: OEM-253260180

[NoYouRelax]

Thanks Ed! I did more searches on "Airbox drain" and it all points to your findings. I guess I will just put a hose on it and route it away from the engine topside. I'm not sure if there is a contraption needed per the earlier years or just a hose.

[RWebb]

use new hoses; maybe clamps & Loctite 518 or something

no RTV

[E Sully]

Part number 12 acts as a one way valve to prevent unmetered air from getting in. I would not use just an open hose, it will suck in dirt and unmetered air. Porsche used this same part on many different intakes over the years. It is kind of a high price to pay for a simple rubber flap valve, so it would not hurt if you can come up with a substitute one way valve.

[NoYouRelax]

It seems that these one way air valves are only called out on earlier models, or were they used on the SC as well? I will install a hose and at least a filter.

[boyt911sc]

Originally Posted by NoYouRelax

I am in the process of reinstalling the CIS system and making every fuel and vacuum line firm and tight. It was very sloppy loose coming apart and old hoses were suspect...RTV and sealant everywhere.

I found a vacuum source, and have yet to find a mating hose for it. It's a connection about 3/8" on the bottom of the airbox. It should be a major vacuum source.....see the yellow arrow in the picture. Any idea what should be connected here?

Bill,

If my vision serves me right, you are referring to the tube underneath the air box (below the air filter)? Most late SC's have these unplugged. This is not critical even to leave it as is. I wouldn't worry about it. It has nothing to do with your engine performance regardless it is plugged or not.

Tony

[E Sully]

I looked at the PET and it seems the rubber valve and hose I showed was only up to 1977. Not being an SC owner I can't add much. It would not be a vacuum leak since it is before the air metering plate, but I can't see the Bosch engineers leaving a port open to unfiltered air.

[NoYouRelax]

Thanks Tony and yes its at the bottom of the airbox. The ID is about 3/16" and it can still draw in particulate....just saying.

Ed,
I agree, its hard to believe its just unfiltered.

[boyt911sc]

Bill,

I used a short rubber hose with one end plugged and slipped to the tube. Or a piece of duct tape would work the same.

Tony

[NoYouRelax]

Well I had to improvise and attach a hose with a homemade (Lowes) filter. I just cant see leaving any unfiltered opening be a source for dust and particulate to the engine, and if it drips oil in the long run, I'd like to see.......it's probably overkill...

[Jerome74911S]

I just took a piece of new hose and attached a bottle to the end of it.

The bottle sits in the engine compartment down in back next to the spark plugs on the right side, and any oil or water that drains collects in the bottle.

In three years I have not yet needed to empty the bottle. I don't know if anyone mentioned, but the name of the missing gadget is a "dribbler".