Shit! There must be something different about those Canadian PC50 units. The ones sold in the US will barely make 30mph downhill with a following breeze.
The only things that I can think that you could do would be:
Raise the compression ratio
Make and install an aftermarket pipe of some sort.
Install a larger carb.
I believe that none of the required parts or pieces are available in the aftermarket, so you are on your own.