Hi all again,
Found the culprits.
1. The Insulator gasket of the DZ200 P/N E2192 is also sold under P/N F2192, although these are two different items, as defined in the exploded view of both engines. I was lucky to find in my drawer the correct F2192, which belongs in the DZ170.
2. The Insulator was wrongly installed with the small cell facing the Intake pipe, instead of facing the air entrance into the carburetor.
Now that the correct parts are reinstalled in their correct orientation, RPM is back again to 7,100 with APC 19x11" and Morgan 30%, and 6,800 with Morgan 20/20.
Thank you all for the sympathy, and always check twice!