Seeing as the previous post actually published, I'm going to attempt an update on my ongoing saga.

I think I've discovered Ground Zero.

I pulled the air filter pipe off the top of the carburettor earlier and it doesn't look pretty. The forward/front chamber's brass jet is absolutely gunged with a black, tar-like substance. The rear chamber's jet is clean and shiny, as it should be, but the diagonal tube near the top is showing signs of corrosion. It looks quite rusty, which sticks out like a sore thumb in an aluminium-bodied carburettor. I'm going to hazard a guess that E5/E10 is to blame. Also doesn't help that a car that was used to doing 10,0000 to 20,000+ miles a year is now lucky to see 2,000 miles between MOTs. It managed only 1,300 miles in the 12 months up to the last MOT in September.

Now, if only this platform worked properly I would be able to illustrate the problems with a couple of photos, but no joy there.

To test image posting

A friend from an oldtimer garage had also this rubbish in the carbs of clients. It was said it could be rust in the tank. But a few of this cars had plastic tanks so this wasn't possible. So he did collect some of this rubbish and gave to a professor of the technical university of Aachen. They tested the stuff and it were indeed iron particles. But they came probably form the refineries or gas stations????

Fingers crossed the two photos will appear below

Is the black not from a backfire?

Oh dear. I've not seen that before. I've cleaned mine out before but only from some random debris.

Jonathan as an aside, you might have one already, but just checking? An inline filter coming to the carb. I've got one of those glass ones. I've not had to change it in years, it's immaculate, I'm pretty fussy about fuel though.

By the way pictures have to be shrunk! It works fine but until I realised that it was very frustrating.

Yes, crop large sized images to shrink them. You don't necessarily have to crop them much to reduce the file size considerably. Or reduce the resolution to take smaller file size images in the first place.

You could just have network issues though!

The issue you found with your carb would manifest itself on both cylinders at the same time, not only on one!

Yeah, I'm certainly getting more of a grasp on what the symptoms are actually telling me. It's clearly both cylinders, but when I pulled the spark plugs out last week the two plugs showed very different signs of what they were doing. One was clean, the other one was definitely not. I think my lack of fully understanding the signs has pulled me back and forth between thinking the issue was battery, ignition drum/barrel, spark plugs, HT leads, the electronic ignition module (123ignition), and starter motor!!!

Fingers crossed that a squirt of carburettor cleaner along with a good prod and polish will resolve the problem and return the 2CV to its usual dependable reliability.

Oh, and I don't now believe the gunge is anything other than the shite left over after the fuel/shite has evaporated.

I also have a see-through fuel filter fitted between the pump and carb. It makes it easy to see if fuel is actually making it's way to the carburettor. It's clean and clear, with absolutely no sign of contamination in it.