Plugging the CIS Mixture Adjustment Hole?
 

What do you guys do regarding the mixture adjustment hole atop the CIS mixture control unit after completing an adjustment? Do you plug the hole with something like the Porsche-recommended shear screw or leave it open to the atmosphere?

Leaving it open isn't problematic to the proper functioning of the CIS because air entering through the hole gets metered by the sensor plate. However, the hole left open is a source for unfiltered air to get into the engine. Is this an issue or a non-issue? Thanks!

Brian

I replaced my decaying engine sound pad, problem solved :)

There was originally a little rubber plug, attached to a sort of wire handle, that was put in this hole.

JR

I made up a little stopper using a brass tube w/ some shrinkwrap tape around the bottom to fit snugly in the hole. There probably are other rubber stoppers available to do this, maybe from a chemistry or plumbing supply outlet.

You're right. It won't affect the air metering. You just don't want crud, say from the sound pad, to get down into the slot of the adjusting screw.

OK, I'm picturing a rubber plug or an allen-headed sheet metal screw with a rubber washer, using safety wire or thin cable on either item to ensure being able to easily get in and out again.

Leaving the hole open (as the car came to me) bugs me. It's like a vacuum cleaner running all the time, pulling dust, pollen, etc. into the engine.

Brian

I use a golf tee.

So maybe I'm over-thinking this. ;)

Brian

Go to a wrecking yard and look for old Volvos that have the Bosch Fuel Injection; lots of 240-series had the wire-handle rubber stopper; that's where I got mine. :)

Hey guys, why bother? When I first bought my 1973.5T with CIS, I could not get the 3mm adjustment wrench down that hexscrew hole to adjust the mixture. The prior owner apparently made the adjustment and sealed the screw with some kind of gunk. It filled the hexscrew hole like rubber cement!!

So, I took off the airbox and had to support the sensor plate with one hand while I used a dental pick to get the crap out with the other. I did this to avoid great pressure on the sensor plate support bar. I finally got it cleaned out well enough to now make adjustments easier. I do not know if the factory sealed these "holes" as they did on say, my older 944 J-tronic. I can see protecting the hole from debris falling in, but thats really about all your doing. Its a hexhead screw that lowers or heightens the sensor plate. I doubt if anything can pass by that screw. If you decide to plug, make sure you can get the plug out and that material is not affected by heat.

Bob
1973.5T Sepia

If it's not plugged, it's an open vacuum hole when the air pump (engine) is running.

Brian

Hey Brian,
No it isn't - otherwise the freshly set CO would change when the plug is reinserted.

Its been a while since I worked on these things, but back in the heyday of K-jet, between 30-50% of the cars I worked on didn't have the plugs anymore. While I'd make an effort to find one if mine was gone, I wouldn't fret terribly if it wasn't there - especially on a 911 where the FD leads a pretty 'sheltered existence' way up high in the back of the engine compartment. Gunters tip with old Volvos is good - VW Rabbits and Audis had similar plugs as well.

Oh, and I just googled "K-jetronic+co+adjustment+plug" and found this

http://www.autopartsfair.com/images/...5018622bos.jpg

at http://www.autopartsfair.com/volvo-engine_parts/catalog-item-415081.html
or http://www.theautochannel.com/autoparts/airpartsvolvo/240items.html

for $12.95. Wish I could come up with something with that sort of profit margin...

That point was settled up high in this thread -- the incoming air through an open mixture plug hole gets metered. No one disputes that. What I'm saying is the open mixture plug hole is a source for unfiltered air to enter the intake system.

Brian

Air Adjustment Plug...
 

I found a plastic cap that slipped over the O.D. of the adjustment housing.

http://forums.pelicanparts.com/uploa...1208359046.jpg

Steve:
What an area to live in!
Drove through it many times, especially the Vosges Mountains; Porsche Roads!
Many memories about Gewuertzraminer - Riesling - Haute Cuisine in Alsace.
And the French mixed with German dialect is priceless.

As for the missing plugs on so many J-Tronics: They come loose and fall off.
I secured mine with a short key chain looped around a line on top of the FD.

Mitch, that's a wonderful solution for folks with modern Motronic-equipped cars.

Gunter, whatever I end up doing, I was thinking the same thing about tie-wrapping or banding the CIS mixture-adjustment plug so it can't disappear into never-never land.

Brian

+1
Mitch: DME doesn't count. :) :D

Sorry Brian, I'm regularly guilty of not reading carefully. What I was trying to say, tho, is that it is pretty much a non-issue. Like I said, I wouldn't fret. But $12.95, while a whole lot of money for a piece of rubber with a piece of wire attached, is not a lot for peace of mind.

Gunter - stop by and say hi next time you're in the area. I'm hoping to have my car-barn finished this summer. Drinking Alsatian wine, German beer, and shooting the Porsche poop are some of my favorite pastimes:D

PM me with your address and I will mail you one.

LM

I've been remiss in not following up on this. LM sent me his spare mixture-adjustment plug! Thanks so much, LM, and if I can return the favor at some time down the 911-driving road, let me know.

What a great place this is!

Brian