You were right guys, today I start the engine. No problem of temperature, when the thermostat opens, water enters engine. It runs just perfect at idle, but impossible to rise RPM !!! I tried with Choke and disconnected choke, nothing to do.
But I'm afraid to open the carburetor. The risk is to never start again ... I try to find litterature on it.
Also, idle is arround 600rpm, the alternator does not charge the battery. But I remember on the friend's X35, no charge at idle, it needed to be arround 1000rpm to start charging. So, I will wait that the engine runs perfectly before deciding to change the alternator.