Peugeot 205 Style 1990 Petrol - lurching and lacking power?

Given that the carb has been cleaned out and you've had the plugs and leads changed, I'd go for replacing the ignition amplifier unit. They can be ok one second and then cause the problems you describe the next second. No easy way to test an ignition amplifier without replacing it. Ignition coil can also provide similiar symptoms but can be tested with a multimeter. Hard to diagnose without seeing the car of course. Good luck.