What hose is this?

In the Netherlands, yur gonna need this system to be working as the temperature gets colder.
Your Factory carb is calibrated to run with a specific air temperature. As the air temp gets colder your carb will run ever leaner, until it starts to complain by misfiring. AND
There is a good chance that right around 0*C to maybe plus 3>5, with high humidity, your carb will go into a condition called "icing"; in the which real ice forms on the edge of the throttles, which upsets the fuel metering, and the engine will slow to a stall.
The heat stove can be doctored with electrical tape or duct-tape, even tinfoil. But that flapper and it's control valve need to also be functioning, cuz they are gonna work together to maintain the calibrated air-temperature. If you take the lid off the air cleaner housing, you'll see the control valve on the floor, on the clean side of the filter.

If your carb is NOT the factory one, then this discussion may or may not apply.