yes you get the number from your key ignition, (little numbers on the flat part where your key goes in)you may have to prove its your bike to the locksmith but thats the least of your worries,i did this too,make a spare and stash it in your toolbox when you get another one cut,you may be wondering that the new key from the ignition numbers seems pretty easy..yeah it is ,lock that bike up with the chain lock that originally came with it or a kryptonite one,this old steel makes for some great parts to the right person. 
We invite you to introduce yourself by a few sentences if you are new to
this discussion group. Enter your e-mail to join the forum and get notifcations on new messages. Or post your question,
answer or comment as a guest. We have just improved this discussion forum and expect the number of users to increase.
More 1981 Yamaha XJ 650 information
Our discussion groups are intended for short messages. We also welcome more extensive motorcycle reviews.
Bikez also recommends that you check out the technical
data and the riders' rating for the 81 Yamaha XJ 650.
You can also rate it yourself. Use our efficient motorcycle
classifieds to sell or
buy
this bike. Your motorbike gets a high quality presentation. Ads are free.