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For informational purpose. I have not tried this myself. That being said; there is a rumor that you can replace the belt on a 440 with a H. D. belt but it seem no-one could ever confirm it. On one of the KZ440 forums I follow on FB, someone has actually found and confirmed that the Goodyear Falcon SPC Rear Drive Belt 1-1/8"  (14mm) 128 tooth belt (Goodyear bdl-spc-128-118) fits. The person put it on and rode for about three minutes. It was a bit tight. Readjusted it and it works so far.

Nope, the teeth are different shapes.
The Kawasaki is a more squared tooth whereas the Harley tooth is more rounded.
I gave up after days of research and converted to a chain.
It could work but I wasn't going to risk it.
photos courtesy of:
Cycle May 1980. Belt drive motorcycling
www.kz400.com/RoadtestsFrameset.html
harley
 
kawasaki

Well dang. I thought it was confirmed. I guess I just I wait and see if he has any issues after riding with it for a bit. 
BTW, I am with you. I wouldn’t risk it either. 

If the pulley teeth fit fully into the belt spaces, I am not so sure those rounded corners would matter.

wrote:

If the pulley teeth fit fully into the belt spaces, I am not so sure those rounded corners would matter.

I would agree with Texas, if correctly tensioned I can't imagine the 400 has enough torque to tear up the belt. However looking at F64's post it looks like the HD belt is wider so will it fit between the belt guides on the sprocket (if it hangs over the edge this will create a weak point at the edge of the sprocket )

From the video he posted, it looks like it fits well width wise.  My 1983 model runs a 1 1/4” wide belt.  From the manual the older bikes run a 1” belt. I am not sure what year that changed. My concern with the rounded teeth is how tall the teeth are.  Is there enough flat on the teeth or are they completely rounded from the base. 

If you have concerns about the belt take a look at the link below,  I used to maintain these bikes and none ever stripped a belt ( even the 110 inch screaming eagle FXDX with 100 ft-lb of torque) even with this Level of abuse. I get the difference in tooth profile but as I said, if it is adjusted correctly I don't see you having an issue (for the belt to slip it has to flex away from the sprocket)

Thanks for all the info. I appreciate it.