It'll spin the starter but won't start the engine. It'll then 'go flat' and not spin the engine. But the voltage is sitting at 12.8v. I'm also thinking of a poor earth due to corrosion or a loose wire/cable/connection. Battery has been pulled from the car and is currently in the garage connected to a smart charger overnight, so I'm covering various bases. I'll see how an overnight charge will go.

Sounds like a job for the cranky handle! Hehehe.

I don't miss having to use that. I spent a year or so without a starter motor at some point when I was very poor.

Yeah, clean terminals before re fitting battery. Check and work your way back through the grounds.

Check the seating and cleanlyness of fuses and fuse holders.

measure the voltages on the wires going into, and out of the ignition switch.

measure at the feed to the 123, and check the ground.

measure voltage at the coil.

do you have fuel being pulled up?

Well I can say it's not the battery. I connected it to the smart charger and the unit didn't throw up a message to say there's an issue. It's sitting at 12.88v. I'll have to go through the wiring and connections to check for anything obvious but, I think the issue can be laid at the door of the ignition contact drum. ECAS sell new ones for £28.80, so I'll add it to the purchase of a new brake master cylinder in the New year.

Some issues what can feel like bad battery..:

-worn bushes on starter
-worn brushes on starter
-commutator of starter, caused by worn brushes
-bad connection of battery terminals
-bad connection on the other end of battery cables, both + and - cables
-worn solenoid contacts on starter

-and, some of these symptoms together, what makes the diagnosing little harder

You can check battery cables by putting the volt meter between battery post, and the other end the cable what is diagnosed. For example, at starter, put the other measuring wire to the terminal of starter, and battery terminal, use the starter and see if there is some voltage to see. If there is over 0,5 V then there could be the issue, and if there is several volts, you sure found the issue. Same measurement with both, + and - circuit, the issue can be anywhere but measuring all wiring You can find it...

If the bushes on starter are worn, the rotor of starter can touch the field, and then the starter takes much more power from battery but gives much less force. Usually there is some strange grinding noise with that symptom...

Borrowed a good known battery I tried it with that. No luck, with the same symptoms as my battery. I've fully recharged mine and refitted directly after failing to start the engine with the borrowed battery... Failed to start I put everything away and was going to back indoors, but returned for 'one last try' and it attempted to fire and start, so I tried a few more times and managed to get it to start... but only on one cylinder. It cut out a few times but was able to restart again, but still only on one cylinder and it refused to idle with cutting out. I had a look around the garage and found an old pair of Eyquem spark plugs and decided to try them. The (UK) nearside NGK plug I removed was clearly showing signs of not sparking, so I hoped I'd found the problem, but sadly not.. with the previously used Eyquem plugs installed the engine started after a few attempts but still only on one cylinder. I've given up for today.



@Jasu, thanks for the check list. The starter motor is not many years old and is a high torque model. I've not done many miles in the car, so I'm going to assume it's all good there. I did discover the 13mm nut on the rear of the motor was a little loose, but tightening the connect hasn't made any difference.

Was it wet with fuel? Try warming some plugs in/on the oven.

Even if you have a wet plug, check fuel delivery.

try swapping the ht leads, does the fault move?

Wipe around the coil and leads with some kitchen towel to remove dust and moisture. Perhaps WD40.

If you have someone to turn the key, check in the dark for arcing.

Trying some WD40 on the coil and HT leads was something I did quite early on. I have a see-through fuel filter in the pipe between the pump and the carburettor. At no point has the fuel been sitting low in the filter, so there must be fuel getting to the carb, surely? The plug on the NS cylinder was certainly wet. I've just gone rummaging around in the garage and found a set of old HT leads which I've swapped for the one fitted to the car. Just like the Eyquem spark plugs I substituted earlier, they've made zero difference. I'm now beginning to suspect the 123ignition module. It's the second one I've fitted to this 2CV, with the original one being replaced after well in excess of 150k miles. This one has probably done well under 10k. What's the forum's thoughts?

I would confirm fuel by detatching the pipe at the carb and pumping into a container.

Do you have plenty of fuel? Is there water in the fuel?

Do you have another coil you could try? One that you know works.

As a test, try closing the gaps up some on the plugs

What charging voltage do you have when running? High voltage (caused by bad ground on v reg), could damage 123.

What is your starting routine ... No choke, pump accellerator. Crank with some throttle. When it fires, add some choke. Push in choke slowly until it runs clean. Drive and remember to push in choke eventually ....

are choke and accel cables set correctly? Is the choke turning off?

Would you happen to still have the defunct 123? I would like to disect one.

Remove both spark plugs and put them back into the HT leads. Cable tie the plug bodies to the inlet part of the manifold.

Crank the engine. Do you get a nice blue spark on both plugs?