Pierre if you're still stuggling there's a product called 'Bradex Easystart'
(yellow,white and black aerosol can) which I'm fairly sure I've seen on sale
at my local Auchan when in Limoges.
It's a highly volatile mix of ether etc which will start most engines as long
as there is some compression.
If you get hold of a tin, remove the crossover pipe and spray directly into the
throttle body whilst you operate the throttle linkage and your friend/assistant
turns the igniton key.
Keep spraying whilst the engine is turning over and it WILL start as long as you continue to spray (it will sound like a tin full of nails because it will firing purely on the Easystart but don't worry)
this procedure will SOMETIMES coax a stubbon engine into life.
Which will then have you wondering 'what was all that about'.
Good Luck.