MOT fail for CO2 - adjusting a Stromberg 175 CDUS

[Bugjam1999]

Hi all,

I have a 1978 245 fitted with a Stromberg 175 CDUS which has failed the MOT as CO2 levels were too high. I haven't done anything to the carb yet, so a starting point is to strip it down, clean it and put it back together.

I can see from receipts from the previous owner that a new jet and needle were fitted in 2011, which equates to about 55,000 miles ago based on MOT mileages. I guess they're due for replacement then - although I'll look at them first to see if there's any obvious damage.

I also have a complete carb from another car which had 90k on it, but I have no idea how good it is or whether the jet and needle in that were ever replaced etc.

My question then - how do I/the garage go about adjusting the carb? I don't have a co2 meter so it'll have to be the garage realistically. I've seen a few threads online, most usefully this one:

https://www.volvoforums.org.uk/showthread.php?t=100472

But I'm not sure if my carb is an earlier or later type, as referred to in that thread.

It looks like this:



Any comments/help/advice? From the thread above I think if the dashpot is removed the needle can be raised up and down to adjust the mixture via a special tool, is that correct?

Thanks

[Clan]

Originally Posted by Bugjam1999

Hi all,

I have a 1978 245 fitted with a Stromberg 175 CDUS which has failed the MOT as CO2 levels were too high. I haven't done anything to the carb yet, so a starting point is to strip it down, clean it and put it back together.

I can see from receipts from the previous owner that a new jet and needle were fitted in 2011, which equates to about 55,000 miles ago based on MOT mileages. I guess they're due for replacement then - although I'll look at them first to see if there's any obvious damage.

I also have a complete carb from another car which had 90k on it, but I have no idea how good it is or whether the jet and needle in that were ever replaced etc.

My question then - how do I/the garage go about adjusting the carb? I don't have a co2 meter so it'll have to be the garage realistically. I've seen a few threads online, most usefully this one:

https://www.volvoforums.org.uk/showthread.php?t=100472

But I'm not sure if my carb is an earlier or later type, as referred to in that thread.

It looks like this:



Any comments/help/advice? From the thread above I think if the dashpot is removed the needle can be raised up and down to adjust the mixture via a special tool, is that correct?

Thanks

There is a brass 8mm nut on the underside to adjust the needle , what was the measured CO at idle ? These carbs were notorious for going rich due to several reasons , The needle and jet wore after about 25000 miles , unleaded fuel is unkind to them , the float
level would rise due to the plastic bridge piece holding the float hinge weakening , also there is a silver valve on the side with a U shaped rubber pipe on , these fail and you get massive richness on choke … they were like this way back when 240's were current , let alone now some 25 years later !

You need to replace at least the above parts and a float chamber gasket and diaphragm for good luck

[Bugjam1999]

Hi,

Thanks - hmmm, doesn't sounds like it'll be much fun messing about with that carb then. I don't know what the measured co2 at idle was, the wording on the failure sheet is:

Exhaust emissions carbon monoxide content excessive (8.2.1.2 (b))

Which I believe refers to the fast idle test.

I wonder if the other carb is any better. Unfortunately without an emissions tester it's hard to tell without frequent trips to the garage.

Thanks

[Clan]

Originally Posted by Bugjam1999

Hi,

Thanks - hmmm, doesn't sounds like it'll be much fun messing about with that carb then. I don't know what the measured co2 at idle was, the wording on the failure sheet is:

Exhaust emissions carbon monoxide content excessive (8.2.1.2 (b))

Which I believe refers to the fast idle test.

I wonder if the other carb is any better. Unfortunately without an emissions tester it's hard to tell without frequent trips to the garage.

Thanks

you are going to have to spend Money what ever you do , best get the current carb overhauled and set up just the once to pass . It should make a big difference to fuel consumption too and sweeter running ..

[Clifford Pope]

It would be worth asking the garage for the detailed emission readings, at idle and at fast test. Normally they give you a separate print out, apart from the certificate or failure notification.

(By the way, it's carbon monoxide CO, not dioxide CO2. CO2 is the complete combustion product if the settings are correct, taking the CO down to the acceptable level)

[Bugjam1999]

Ok, I’ve dug out the paperwork and there is a specific figure given- the co (not co2, thank you) reading was 6.09% and the limit is 4.5%. There was only one set of figures given, I presume for a car this old it’s only tested at fast idle?

Anyway, since that’s significantly over the limit I imagine anything short of sending the carb away to someone who knows what they’re doing with it would be fairly futile...

So I’m going to swap it completely. I’ve got a manifold fitted with a Weber 22/34 dmtl that I bought from a forum member a little while back, it was on his b21 equipped car and was set up properly on a rolling road so hopefully it’ll bolt on and work with minimal fuss.

If I didn’t have the weber sitting there I’d put more effort into fixing the Stromberg, but in the interests of time - optimistically booked mot on Friday, car show Saturday - I’ll swap the Weber in and hope that works.

Also- from the looks of this thread others have been happy with Weber conversions to redblock engines...

https://www.volvoforums.org.uk/showthread.php?t=155444

Cheers