Right, so as mentioned my car failed it's mot again on emissions, with 6.5% CO. Nothing I could adjust at the test centre made any difference, and to be honest I am pissing in the wind a bit here. Now, the mixture screw, as I understand it is the one on the front of the carb withthe offset slot? On my car it'd been mangled in and wouldn't screw in more than a few threads and went in pissed. I changed the carb for a random one off the scrap pile/carefully stored spares. I briefly cleaned it out and fitted it, after starting it I tried to adjust the mixture and noticed that I can turn the screw a couple of turns either way and the engine stalls is that normal? Where do I start with this?

Secondly, would the high CO have anything to do with the new rings and pistons etc? Ie, as it's not run in yet I assume it's probably burning a bit more oil than it should, or something...

Has it had a good run russ? Maybe if (wild card) there was a tiny bit ofnoil through valve stems it is not all burnt off..?

Russell,
when the idle mixture screw is correctly adjusted, any more than about 1 to 1.5 turns inwards should make the idle uneven (because it's too lean), whereas it should take about 3 or 4 turns out to make it stumble because it's too rich.

Engines are much more sensitive to a weak mixture than a rich one, which is why folk don't tend to notice that their air filter is clogged, until they bother to do an mpg check, that is...

With the 2CV's long inlet tracts, you should wait about 5 seconds after turning the screw to see what effect it's had, since movement of gas through the tracts is slow with the throttle closed and only the idle circuit in operation.

Sean will have the link to a VW video, showing how to adjust the idle on their Solex carbs.
With it warmed up, turn the idle screw inwards until the engine falters, then back about 1/2 to 1 turn.
1/2 is better if you're struggling with the MOT emissions test, so bring the idle speed up a bit to keep it running OK.

Lastly, new barrels and pistons do need to be run in.
Is it too late for this?
http://www.citroentuning.de/doc/How_to_break_in.pdf

ken

( High CO tends to be mixture too rich, high HC is related to oil getting into the combustion chamber.)

Thanks, I watched sean's video but I didnt know if what I was doing and the results I had were what I should be expecting. I'll take it back in as it is now, and if it still won't go down I'll have to rethink things a bit. You've put my mind at ease a bit though, thanks.

The BB had a reading of 0.5% CO two weeks ago at its MOT so you should be able to get down to this sort of level....have you checked the needle on the idle mixture screw? They get easily flattened on the end and wont make a good connection in the body of the carb..If it screws in fully and the engine still runs then probably knackered...otherwise screw in, back off a couple of turns then adjust the revs using the throttle stop screw and then play around to get smoothest running

UK cities face ban on heavily polluting traffic. Is this likely to affect 2CVs?

Doubt it. I think stuff like this is mainly based around stuff like big diesel buses/trucks and the like, that don't have the newer engines that the EU now insists on stuff having. Could be wrong though, although compared to some countries like Belgium and Luxembourg we still have really slack legislation as the British Government never seem to have been one to go right into bigging up the EU. By default I'm guessing that this spans accross all kinds of legislation, even stuff like this. In Belgium I know that you've got to tell the authorities weeks in advance if you plan to go anywhere near a town with your old polluting piece of shit car. Its all bollox really, talking of which I'll stop talking it.