Looking for CO2 adjustment screw

Hi

I’m urgently looking for the CO2 adjustment screw for a MK1 Golf GTI (1983) which I believe is a Bosh K-Jetronic system. The part number may be 067133432A (TBC) Any help/advice you can give me would be much appreciated.

I have attached a photo showing where it is located - it's inside the tube that is identified with the red arrow. I've also attached a diagram that gives an indication of what it looks like.









Ian

I'm not sure if you can buy just the fuel mixture adjustment screw inside the metering head.

068133432a is the idle control screw at the back of the throttle body.


https://www.lllparts.co.uk/product/volkswagen-067133432a-adjusting-screw/mpn/067133432a

I can't find the part number online as most free sites don't list separate parts of Bosch Metering head.

You're presumably having issues with yours?

If your set up wasn't so clean, I'd suggest it's maybe that the socket head of the screw has become clogged and not allowing the 3mm adjustment key to seat properly, though might be worth checking regardless and an easy fix.

If it's not that, has the hex socket rounded out so that the key can no longer turn it?

It's always possible Bosch supplied them as spares, though I wouldn't hold out much hope of finding any nowadays if they did.

They're made of quite a soft material, which is likely part of the reason why they can be so easily damaged.

If you're handy and are able to remove your existing one it's possible to fix them, though that's obviously dependant on the extent of what's happened to it.

An upside of it being soft material is you can reform the hex by pressing a slightly bigger key / allen socket or similar into it.

 I used a 1/8 SAE bit on this particular one as that's just ever so slightly larger than 3mm, but if the damage is greater perhaps another size up may still work.

Probably your only other bet would be to scavenge one from another air flow sensor, but you're relying on it not being damaged also.

If you do go down that road be aware the screws in later air flow sensors had a much finer thread and aren't interchangable with the one you'll likely have.

I think the change was to allow for more accurate adjustment, but I'm not aware of when the change over point was.






 

Hi

The screw is missing from the car. I only discovered it when I had the camshaft changed from a lifted cam to a standard cam and, as a result, needed to adjust the CO2 mix. That's when we discovered the screw is not there!

Do you have a specification for the screw so that I can get it made?

Thanks
 

Curious to know how the engine ran without it previously!

… or maybe it didn't?

Is that your unit in the image, if so looks to have been refurbished?

Brings a lot of questions to mind but rather than me trying to guess, can you elaborate a bit more?

For example, have you had the mixture control unit off and are able to see the adjustment screw is missing or is there something else in its place?

Images are useful too.

Ho-Hum… why do I bother trying to help?

The car had a lifted cam in it when I got it. I recently had it changed to a standard cam and it was running rich. When I took it to a tuner he told me that the CO2 screw is missing. Presumably the mix without the screw was OK with the lifted cam but not with the standard cam.

It still runs but, as I said it is too rich. I need the screw to get it running properly.

I'm struggling to see how your engine will run if the screw is missing, but the person who looked at it has the advantage of me having had it in front of them, so I have to accept it must be possible.

Below are some photos of the main parts of a near identical airflow sensor to yours.

That smaller arm (with the screw in) sits within the larger arm and both are fixed to the units main body by a pivoting bar (not shown).

I've intentionally taken the images the way I have to try and show where each part is located in relation to the others, if the entire meter was fully assembled they may appear slightly differently.

Maybe you can see that the pan head of the screw pushes into that two pronged holder of the larger arm.

It's a very tight fit, if you ever have to remove one it takes a bit of effort to slide out.

I'd contend it's not going to fall out of it's own accord, if it's missing, it's because it wasn't put back / back correctly.

Because it's held so rigidly there's no possibility that the smaller arm can move about, the screw effectively keeps the small and large arm in a fixed relationship to one another at its end and the pivot holds things secure at the other.

The only way to change that relationship (as happens when adjusting the CO) is to turn the screw.

If the screw is missing it will no longer be a rigid set up and the smaller arm will potentially move up and down out of sync with the larger arm or maybe not move at all, just rest on the lower arm?

That shiney roller near the pivot end of the small arm is what the fuel distributor plunger rests on.

If the relationship between it / it's movement and the arms plus the screw isn't correct I'd be amazed it can run, let alone even badly.

I've read posts where the writer thought the screw was missing because they couldn't see one in the access tube.

The screw is way down inside the airflow meter, a long 3mm allen key is needed to reach it.

Back to your original post - Where did your diagram come from, it's accurate in a very general way but could be misleading if you think that's how the screw is positioned?

Without images or better info. I'm afraid I'm just stabbing in the dark here.

You don't need to strip it apart, but a view of the airflow sensors underside via the air filter side of things showing the arms may confirm the screw's missing or not, if it is we can maybe take things from there.

The last image maybe gives you an idea just how far below the bottom of the access tube the screw is.












 

This is a 6 cylinder control unit from a Porsche but the airflow sensor is more or less the same make up as on the MK1.

Might help in seeing where things are in relation to one another.

Note there's no access tube pictured on this one, just a hole directly into the upper surface of the main casting… again I've read posts where it's assumed the screw is missing when in reality there's a bung (8) there instead and the screw is much deeper down / part of the small arm.

Now that I see this it maybe suggests the screw wasn't available on it's own as it's unnumbered, merely as part of an assembly along with 11?

bacardincoke said

This is a 6 cylinder control unit from a Porsche but the airflow sensor is more or less the same make up as on the MK1.

Might help in seeing where things are in relation to one another.

Note there's no access tube pictured on this one, just a hole directly into the upper surface of the main casting… again I've read posts where it's assumed the screw is missing when in reality there's a bung (8) there instead and the screw is much deeper down / part of the small arm.

Now that I see this it maybe suggests the screw wasn't available on it's own as it's unnumbered, merely as part of an assembly along with 11?

I have a couple lying around could put some images on if it would help

Sent from my SM-G975F using Tapatalk

Sounds like Ian would take one from you!

I can measure the one in my images if it comes down to making one though it'll be by using a cheap vernier so not ideal for such an exact part.

Thanks for the info. I'd need a pretty exact spec - length, diameter, thread count.  I've attached a diagram showing how it fits (I think!).

Thanks for the photos - they are useful. Is the 'screw'  adjusted using a 3mm Allen key - so it will have a 3mm hex indent in the head?
 

Thanks for the info and the photos - they are useful. I assume the screw will have a 3mm hex indent in the head to take the Allen key?
 
It looks like I may need to get someone to take the whole unit apart!

As you may have guessed, I'm no mechanic so all this is a bit overwhelming to be honest.

Yes it does have a 3mm hex indent, a reasonably long, standard allen key should reach.

When the time comes and you're setting the CO,  remove the key completely from the airflow sensor after every adjustment and before you rev. the engine, it'll cause damage otherwise.

This is probably going to be slightly easier said than done as your airflow meter / fuel distributor will still be connected to its lines and hose and the one pictured is off the car, however it should still be doable.

Try undoing the airbox clips and carefully lift the upper part away without putting stress on anything, just as you would if you were replacing the air filter.

You may be able to see (maybe with the help of a mirror if there's not much of a gap) the underside of the unit.

Yours looks very clean on the outside, so hopefully if the inside's as equally clean part of the adjustment screw (if it's there) and the small arm it's held in will be visible.

There's no need to dismantle anything else at this stage until we know if the screw's there or not.

These a poor images,  but hopefully show what you're looking for…





 

Thanks again for the advice and the images.

I'm going from the word of the tuner who I gave it to to set it up. He is an experienced tuner and is familiar with the Golf.

It was him that said that the screw is missing - he said that the Allen key was going straight through.

Hi,
When you get your head around kjet it really isn't that complex but it does take a while to work it out.
I think and I could be wrong that if that screw were missing the mixture would be weak, not rich, and before the screw evaporated into thin air you would have noticed the car running rally badly.
I would check the valve timing, if the trouble started after the cam was changed that would be a good place to start.

Can't fathom why you're so reticent to look for yourself, no point going down some rabbit hole looking for, or getting a screw made when a couple of minutes will settle it once and for all?

It's not about doubting your tuner,  if it were me I'd grateful to have another pair of eyes look at the issue.

If it is missing you're going to have to strip the airflow meter to fit a new one regardless.

Anyway… do let us know how you get on, it's an interesting one and would be keen to learn the outcome.

 

This may sound like a stupid question but how do I 'look' myself. How do I know if the screw is there without taking it apart? I've ordered a long 3mm Allen key and I'll try that to see if I can feel it.  Is there any other way to tell if it is there?