Carbs

I measured the inside diameter of the inlet that connects to the rubber boot on the reedcage (I guess thats the "intake manifold")

Mine measured 36mm. I then looked up the number of my carb and found it was a Keihin PWK 36mm Airstryker.

Measure the side that goes to the engine and not the side the air filter connects to.

Unless Im wrong, if so, someone please correct me.
 
You're correct, you measure the rear end of the carb where it connect to intake.
What's all done to the motor to require suck a big carb?