[fizeus]

Ciao Luca,
An Italian Pelican is here!!! (from south Italy).
You didn't tell us what spark plugs you used and how they are gapped.

I had similar problems and i discovered that the gap was was out of spec.

Also,
how does the car starts up (cold and warm)... if you feel it difficult to start up it could be a distributor timing problem that has emerged with the spark plugs/cables replacement.