CO2 adjustment screw, dumb ass question?

Hi,

dumb ass question but aren’t I supposed to have a 3mm hex head adjustment screw in this hole?
And if so, have you any idea where I can get 1 or what the thread size is?

Regards Rob

 

I's it K-Jet?.

Mine needed the top digging out, had some dirt in it.

The allen key is below the top of the metering head. I used a long Snap-on one on 1/4 drive.

 

Hi Kieth,
The screw isn’t there as you can see from the picture it goes down to the flap inside. When I drop the Allen key in, if I push down the engine note changes and visa Vera.

 

Time to take the top off and have a look to see if you still have the screw!

 

I’ll be amazed if it’s there, from the state of the hole it’s been missing a long time. I’ve checked an old MOT from 2015 and it’s CO2 was 0.19% so it’s been running lean a long time , though that was the last MOT.
I’ve spent all night trying to find a part number but with no luck so will take it apart tomorrow to measure the hole and take it from there.

 

The adjustment hex screw is accessed via a short metal tube that's seated in that hole on the casing , though the tube looks to be missing from yours.

The adjustment hex screw itself is part of a pivoting arm much further inside. To give you an idea of how far in I'd guess it's likely it you are pressing on when you say your pushing down with your allen key can cause the revs to change.

Is it that you're maybe under the impression the hole in the photo is threaded and that's where the (missing) adjustment screw is situated?

Be careful, it's possible to damage the internals by revving the engine with the allen key still in the adjustment screw, it's to be removed between every adjustment as it'll interfere with / prevent the action of the pivot arm.

 

Have a look at the 'Kjet strip down question' thread by Cressa of a few weeks ago, there's some good images that might show you what the adjustment screw looks like and where it's sited. I'd be surprised if it's missing, though it may be rounded out or possibly moved out of position?

 

Thanks for that and it makes for some good reading. As the cars been off the road for so long I may as well do a complete overhaul of the kjet system. Are there any step by step strip down write ups or is the cressa post the best to follow?

 

Plenty of info out there. Zender Z20s info is what gave me the courage to 'go for it'.
A guy called grey goose on you tube has done some video's which I found helpful too.
Is yours an 8v or 16v?

 

Hi Cressa,
Mine is a 16v, spent some time surfing the net and like you say there is loads of info out there and that what’s confusing at the moment, I need to find the 1 relevant to the mk2.
I found a very informative cross section diagrams of the metering head that explains why people were saying the adjuster will still be there. Where as I saw the hole and only the hole, I dint think it would be inside the hole. So tomorrow I’ll be straight in there with the 3mm twiddling away. With a CO2 reading of 0.8 I have plenty so wiggle room.

 

Morning,
To late for that now, it’s out and on the kitchen table.
Have you any idea of a part number for the adjustment screw or where they sell them?

 

As you can see from the picture below the screw doesn’t look the best so it’s off to work for an 8 hour soak in the sonic bath. After that I’ll see where I’m at but probably a soak plus gas for 24hrs then give it a try.

 

I picked up a cheapie airflow regulator for the MK1 that had it's adjustment screw rounded out.

Later I got a Volvo 240 one thrown in with something else I was after, and have since been using it as a guinea pig and parts.

What I can tell you is the adjustment screw is the same on each... I used the Volvo's to replace the VW's.

Unfortunately I can't vouch for other regulators, but if you're really stuck might be worth looking into.

I sort of fixed the rounded out one, was experimenting and didn't want to just bin it, might be another option if you're really, really stuck.

They seem to be made of a reasonably soft metal, probably why they fail.

If you've a socket set with SAE sized bits the 1/8 hex is just oversized for the 3mm hex hole.

Use a vice or similar to press it in and it will reform a slightly bigger hex head on the rounded out screw.

A 1/8 hex driver will still easily fit in the access hole / tube.

If you're really, really, really stuck drop me a PM and you can have the 1/8 enlarged one in the piccie.

 

Not sure if my co2 screw turns at all. With engine off (obviously) and plastic air pipe to throttle removed would the air plate be seen to rise/fall when the screw is turned, as that would give a good indication?

 

I'm still getting my head around Kjet so nothing I say is written in stone here. I'm thrashing it out in my head too and there's no guarantees I've got it right...

I'm also going to be a real pain in the arse from now on and start calling things by their proper title, I've been as guilty as the next person of using multiple names for what's the same thing and confusing myself plus likely others as well in the process... so just shout if something's name isn't familiar.

Likewise if I've misunderstood anything, only too glad to be told as that's all part of learning.

So, if I've understood correctly, the mixture screw influences the relationship between the air flow sensor plate and the fuel distributor control plunger.

It adjusts the air / fuel ratio by increasing / decreasing the amount of fuel and not the amount of air.

The air flow sensor plate won't move if you adjust the mixture screw, it'll instead cause the smaller arm it's seated in (the mixture lever) to rise or fall while the larger arm (the sensor plate lever) will remain unchanged. Think of it as a separate small lever within a larger lever.

If you turn the mixture screw clockwise it'll cause the mixture lever to rise and because the control plunger rests on that shiney roller at one end of it, it too will rise.

That increases the amount of fuel, but the air flow remains as it was before - ie. you get a richer mixture.

While you do all this adjusting when the engines at idle, the same change in relationship between air and fuel is replicated throughout the rev. range.

Long way of saying, no you won't (shouldn't) see the air flow sensor plate move when you turn the mixture screw.

If the whole lot were back together again you might just be able to see or feel some movement of the roller at the end of the mixture lever (that the control plunger rests on and is visible through the large hole the fuel distributor fits into) as you turn the mixture screw, but it's got a very, very small range of travel so going to be hard to detect.

 

Cheers for that zender, works sonic cleaner was no more than a 75 degree bathtub with no chemicals in, so came out the same as it went in. I’ll have a look at pressing the 1/8 in in the morning but don’t think I’ve got that size. What I was think, was along the same lines, using a torq 25 in the same way. As it’s still seized in there is it solid enough to have that sort of force put through it while it’s still in there?
I have emailed a seller that has just the ally part on eBay for £30 to see if the screw if free but other than that they are going for silly money.

 

Thank you Zender that explains it very clearly.