Quick up-date - I have re-checked the timing, using both rod int'ole method and strobe - it was more or less bang on and advance weights were doing their job OK. I have now backed advance off a little - maybe 6 teeth, rather than 6.5, and the pinking has stopped.....

He he the word is soot, thanks Sean. No no I won't knock or pinking you

pps, "V" in the case of slapping this time is "my" V who is a chemistry teacher, organic chemist and university tutour.

as soon as she see one of her students quoting "Wiki" the paper is thrown back with a strongly worded rebuke

best part of Wiki is to trawl through the references at the bottom of the page

Oh OK maybe she needs some piston slapping

Joolz,
seems as though some progress has been made, whilst I've been having fun hauling a gearbox out of a Dyane and starting to strip it down...

A lean mixture will burn both slower and hotter than a stoichiometrically correct mixture.
Modern engine management systems automatically correct the mixture to compensate for the 'leaning' effect of the additives in unleaded fuel, however a carburettor needs to have its jets changed to make the same correction.

Rebel2cv's 'lean misfire' problem is a perfect example of this, especially as he's made matters worse by running with an open air filter and 2 into 1 exhaust...

Note that for peak power, the mixture should be 'around' 10% richer than stoichiometric...


As regards that quote earlier... "Detonation exists when the combustion pressure is raised so high that the inlet charge ignites itself before the spark plug fires. When this happens, combustion takes place while the piston is still travelling up in the cylinder"

...I'd add the second sentence as well, since combustion needs to be taking place whilst the piston is travelling up the cylinder, in order for peak cylinder pressure to be achieved around 10 degrees after top dead centre.
In an A series engine, combustion of the mixture is initiated at around 8 degrees BTDC at tickover, with the amount of ignition advance increasing to something over 30 degrees at full chat.

ken.

Btw, there is a 'Masterclass guide to 2CV ignition' on the internet.
If you want to take a trip to the dark side, consider these gems of advice to be found there...

The concept of timing is pretty simple and it is effectively the lead-time that is required so that the time difference between the “signal” for the coil to fire being sent (points opening) and the spark plug actually firing is catered for.

What on earth is that about?

Pre-ignition occurs when the signal is sent too far in advance and the spark plug therefore fires before the piston reaches top dead center.
Imagine the forces involved when the engine is revving at 6,000 RPM and the rotational forces of the engine are pushing the piston back up to top dead center to compress the mixture and the spark plug ignites the mixture!
Bad news.

No kidding?

Having the timing too far retarded is also not that great because the piston will be on its way back down the bore again before the mixture is ignited and the maximum energy will not be reaped from the explosion.

Whatever happened to that 'controlled burn'?

Damn it, I knew that air filter was bad news! Only put it on to upset a guy at work( he told me it wasn't possible) I've been meaning to change it back fir ages. So ken are you saying mine is due to mixture??

I didn't say change the weights ... I said check 'em. Then change them if they need changing.

aye blowing a hole in your piston would really show him!

so now d'yall believe me when i say you cant simply change the exhaust or filter( to a lesser extent ) without ajusting the carburation

Never heard you say that tbh, air filter was my fault, but the exhaust was all I had to hand when my crossbox went- soo not my fault haha

exhaust pipes "back pressure"( or lack there off) ,tuned lengths and the like 2/1 exhausts twin exhausts etc etc

usually with the caveat of " the guys at citroen paid more than us and with much more understanding than us got it right" " youll have to go a long way to better the original set up"or words to that effect here, over there..... and on some other forums for dinosaurs( ie 10 yrs ago and no pictures )