CIS Mixture adjustment
 

I tried to see if I could adjust the mixture through the hole in the top of the fuel distributer with a 3mm hex wrench. The wrench would not budge. Could it be that the adjustment screw is frozen, or do I have the wrench in the correct location?

it is hard to find that slot, but once you find it, it should turn very easily. If it would not budge, then maybe you have not seated correctly. When was the last time anyone did this on your car?

It has been a few years now since it was last adjusted. I know that the wrench was seated firmly in something as it was very solid.

I had the same problem, that is, the wrench put some kind of locktite on top of the screw to hold it permanently!

The first thing to do in your case is to remove your air filter cover and hold the sensor plate firmly with one hand. Careful!! DO NOT bend it. Then try to lightly push down on the adjustment screw and see if it moves or even feels like the 3mm adjustment tool is in the slot. If its not then the slot is filled with junk of some sort, so the easiest thing to do is use a dental pick or tool that will get in there and loosen the stuff up. I used a pick and a mini-vacuum. You could use compressed air as well.

Its a slow tedious process, but the results will pay off with patience.

Good luck

Bob
73.5T

Originally, the Bosch FD had a rubber plug keeping the dirt out of the little hole. Over the years, many cars are running with the plug missing.
The little Allen set-screw can fill up with dirt.
I would spray some penetrating oil into the hole so some will get onto the screw. Then clean out the hex with a slim picking tool.
Take the air filter out and carefully hold the air sensor plate mechanism while fitting the LONG 3mm Allen wrench.
The wrench has to sit firmly in the hex; the mix adjust screw is very important and needs to be handled carefully.
Do not leave the Allen wrench in there when revving the engine!

Did you ever get your mixture screw "unstuck", Cipotifoso?
I have a similar problem with my '79, and am starting the dismantling tomorrow to investigate. It definitely feels like it has locked in, but won't move either direction and it isn't a place where excessive force should be used.

I have several pic's of the mixture screw assembly, but none of what the actual screw head looks like - is it a hex head similar to the spring-loaded 3mm one? Some have mentioned getting it to sit into the "slot". How many "slots" are there if it isn't hex?

It's just an allen head screw..

See here:

http://forums.pelicanparts.com/showthread.php?s=&threadid=185926&perpage=20&highl ight=cis%20mixture%20idle&pagenumber=2

CIS Adjustment
 

I had a similar problem the 1st time I attempted to adjust the A/F mixture on my 930. Turns out that there was a small metal disc covering the allen head adjustment screw that was apparently there since the car was built. I used a small metal pick to remove the disc. I hope this helps.