High fuel consumption Piaggio Quartz

Moin, I have a problem with my Piaggio Quartz 50 scooter. The fuel consumption is about 7 liters. We flushed the carburetor with brake cleaner and installed another spark plug (Champion rn2c). After that the scooter ran a little better but the consumption has not improved. Does any of you have any idea what it might be about or a solution proposal? lg