This should answer all your moped questions...
The jet is the conical part that creates the harmonics inside your Biturbo, in effect stimulating the formation of the twin vacuum vortexes to form, that the Biturbo is so famous for. If the jet is pointed upward more inside the stinger (up jetting), the vortexes go against the Coriolis effect for the northern hemisphere, raising engine RPM, for immense low end speed. They (down jet) for more power in Australia, because Australia resides in the southern hemisphere.
It's important to up jet..especially if your bike is from Australia; like all the Puch mopeds.
I think this will help you...