If something is syrupier, it has more syrup in it or tastes more like syrup.
Syrupier things might be very sweet or sticky.
Examples:
The pancake is syrupier than the waffle.
I like my juice syrupier than yours.
The syrupier the better, I always say.
This candy is so syrupy, it's almost syrupier than syrup!
Her voice was syrupier than honey.
The air was syrupier than usual, and everything felt sticky.