struggle starting

Hello

I have a Spark 1.0 2011.

I recently replaced the spark plugs with NGK (0.7mm) spark plugs and replaced the spark plug wires (NGK). I have the cables in this order: 1.3.4.2

but the problem is that the car sometimes has trouble starting. It starts every time, but it struggles a bit when the engine starts. Give it a little throttle once or wait a few seconds and the problem is gone. This only happens when the engine has cooled down.

any idea where to look? I also tried the old spark plug wires but it didn't help.

thanks.
Marco