These front sprocket nuts are a real problem it seems. As I mentioned in another post on here my 2003 FZS600 foxeye still has the original 9mm nut fitted, I have the upgrade kit 12mm nut and washer on the bench in my shed ready to go, but, try as I may I cannot undo the one that's on the bike.
I have straightened out the lock/tab washer 32mm socket with 500mm bar and put all the pressure I can on it, had a mate sit on bike, in gear, brakes on and fucking near burst a blood vessel trying to loosen that bastard to no avail. One of the other foccers in here came up with the solution which I have yet to do, that is ride down to a friendly mechanic pop the sprocket cover off the bike and get him to put his air/impact wrench on it, nip it back up tight by hand ride home and complete the task. I thought KingKong was an American but the cupid stunt worked for Yamaha in the front sprocket nut department when they built my bike.
But what a great bike they are though, great for pottering about in town and great for tear arseing about down country lanes, basically a brilliant all rounder with a nod towards the retro look, I love it.