if it's a standard Saturno it should run with the standard jetting given in the manual.
HP always is thinking about racing Saturnos first
Did you have a 'german' version or an italian?
If you don't know it can be testet at the exhaust outlet.
Sometimes there are converted versions out there.
Some people remove the little tube at the german exhaust damper and never modify the inlet rubber or/and the jetting.
I found this at several german Nordies converted from 27HP
So maybe it's worth to have a look.
You know the different jetting from the manual i think.
The rubber has to be fully open. In the german version there are some of the small rectangle parts closed.
If your Saturno is running fine on idle with the screw out only one turn, it should have either a to big idle jet and/or a wrong (to high) fuel level.
At least i would suspect this. But i may be wrong