How much CO2 does a motorbike produces every km?

Doesn't the driver ( and any passengers ) in the car emit CO2 as well, so you are not comparing like with like.

You must compare CO2 from Car, driver and passengers with CO2 emitted by cyclist to be more accurate.

You will need to divide the CO2 for car driver and passenger by number of occupants of car to get CO2 per person per journey