I am not that sure that it is fuel related, as this only occurs when the bike is not warm, and only on low gears. Higher gears with the same (low) RPM don’t seem to behave in the same way, the acceleration is smooth there.
Also, I am pretty sure my bike is fuel injected as there is no choke, and the instrument is the “newer” type with FI light etc, but I might be wrong as I am only now starting to dive into motorbike maintenance and how they work in general.