stuck in neutral..

so i was out for a ride today and all of a sudden my bike went out of gear, like the clutch was in. I pulled over and shifted into first, but no movement. The bike just doesnt seem to want to go into gear. Anyways i called a friend to pick my bike up in his truck, and when i got home and moved it into the garage i noticed a clicking noise sort of like a mountain bike makes when you arent pedalling. any thoughts?
ps the bike is a 77kz650

Sounds like you spun the nut off the front sprocket. If so, make sure you bend the lock tab down after you tighten it.

well i just checked the sprocket and sure enough the nut was gone. Thanks very much for the help. now for my next question, what size of nut is that? i check z1enterprises and they do not have any.

According to Kawasaki. For a KZ650-B1 (1977), it's a 20MM nut. Part number 92016-028.

perfect i got the nut. last question... is there a specific tourque setting that is used here or should i just tighten the thing as much as possible?

I believe its 60 ft-lbs, but someone else might have the actual spec.

Just be sure to use some blue thread locker, and it will not likely come off again until you ask it to.