what i'm about to ask has no doubt been covered at length, possibly hundreds of times before. I haven't got the time to trawl through unfortunately, so i'm hoping someone can help a brother out!

The van appears to be running lovely, but it seems to be kicking out a lot of black soot? from the exhaust when i rev the engine. The tickover's good, it's quite responsive, starts easily when hot & when cold.
The plugs are fouling up quite badly & it smells like it's running rich. I've adjusted the mixture screw & cleaned the plugs, & driven appoximately 25 miles & checked again; still fouling up.

I haven't as yet checked the float height. Could the needle valve be blocked by dirt? I have a spare carb here, but are Acad/Dyane carbs jetted differently? Will late model twin choke 2cv carb work ok?

I'm a bit worried as i'm driving to Portsmouth on Monday & then bound for France.

Any ideas, gang?

I might add, that there appears to be mayonnaise on the lid of the breather, and IIRC from another thread, that's a sign that the rings are worn? Just thought i'd mention it as it might have a bearing on what's up!

This will probably be no help mate, but the choke isn't stuck open at all is it?

Nah, i did check!

Neil whats it like without the air filter

Hi Simon, it doesn't seem to make any difference...

The spare carb i have has the marking '26 18' embossed on it, as does the one currently on the Acad, I've just had it to bits (the spare) and the float level's 35mm! The book of lies reckons it should be 25mm? That's taking in to account the carb gasket & measuring to the top of the floats. I thought the float measured from the base to the 'dimple' in the middle of the float?

The choke pull off device - is it worth binning? if so how? Do you just take the two scews out, bin the device & whack the screws back in to blank it off? or is it more involved?!

Neil,
is the existing carb an 18/26 version of the 26/35 carb, or is it one of the older 21/24 jobs?

Unless someone's been monkeying around with the jets, the 18/26 type should have a 102.5 (or occasionally 105) primary petrol jet, with the secondary petrol jet being 87.5 or 90.
This applies regardless of whether the carb was installed on a 2CV or a Dyane/Acadiane.

However, in most cases, I've found that on a 2CV, the primary petrol jet will need to be increased to 107.5 to correct a _lean_ mixture on the primary choke, whereas engines with 'forced induction' setups need a 110 jet.
The difference is because the slight increase in air pressure from forced induction is enough to depress the level of fuel in the emulsion tubes.
Carburettors are sensitive to air velocity, but not air pressure...

Short version of the above..
I'd be very surprised if your van was running rich on standard jetting.

Possible causes of it running rich might be if someone has fitted the primary petrol jet from a 21/24 carb. They're either 120 or 125 and are far too large.
The mixture screw shouldn't have any significant effect above about 1/4 throttle, unless it's wildly out.
Ditto for float height, which should be measured from the gasket to the 'pip' on the centre of the floats. 18mm is the usual setting, but I prefer 15mm, so there's more fuel in the bowls and less chance of it cutting out round long bends...

ken.
( To get rid of the 'choke pull-off device', you need some shorter screws to fit on the lid, otherwise the originals may foul a float.
The tiny drilling through which vacuum is transmitted to the device needs to be plugged, with a thin self-tapping screw working quite well for this purpose.)

Thanks for the reply, Ken.

I'm a carb novice, i have to admit. Checking float height, cleaning the float bowl out & unblocking idle jet's all i've really done! Anyways, I've been out and had a gander at the spare carb & this is what i've found:





I'm guessing the secondry jet is the one in the float bowl? what does 2AA & 1.F2 relate to?

* the choke pull-off removal blanking mod isn't complete!

Neil,
those are the air corrector jets, which are screwed into the top of the emulsion tubes.
Usually trouble free, just make sure they're tight.

If you're removing the cpod ( to save typing 'choke pull-off' device every time) M5 nuts fitted under the head of the original screws can be used as spacers.

ken

I think you find the primary main jet, that Ken was talking about, at the bottom of the float bowl directly underneath the jet that you've labelled 'l.F2'. Similar looking to the one marked '87.5'

AH! i did wonder, i've just been out searching for it! So i guess you unscrew the emulision tube to gain access & then in turn unscrew the Main? jet that's underrneath? I've got an old 'Autobooks' manual & that seems far more useful than the book of lies. Pity the exploded diagram is sooo small, or it have been even more of a help.