I also own a Buell thunderbolt along with my KLR. It's a 1200 sportster on steroids so trust me when I say the only thing cheap about harley parts is their construction.NewRiderKLR600
The KLR600 and all 650s use the Keihin CVK40, so yes.
Harley Davidson Sportsters also use a version of the CVK40. I think the prime difference is that the Sportser version has an accelerator pump. HD charges a whole lot less for spare and replacement parts than Kawasaki does.
You might want to go to the HD store and see what they want for a diaphragm.
Welcome to the forum!