Loss of power

I have a ‘79 kz650b and when I get it to about 70-80 mph it loses power and starts to bog. I put a new stator on it and the same thing happened. I’ve heard that it needs one from an ‘80 because it puts out more power and that I should change the regulator. Any ideas? Thanks

Welcome to KZRider Wiscolowlife!
Seriously doubt that your problem has anything to do with electrics.
Check first:
Gas cap vent is blocked?
Compression ratio?
Valve adjustment?
Good luck keep us posted.
Bill
 

Yes, perform all maintenance as described in the real Kawasaki service manual.  Also, is the bike stock or did you install pod air filters or anything else?  Mods like pods can cause problems like you describe.