Caliper Spacer

[royxxx]

1977 XS650, I have had to fit 1mm thick washers between the left calliper & the fork leg to centre the calliper on the rotor, anyone else experienced this anomaly ?

 

[XSLeo]

Sounds like you have a rotor from some other bike. The offset isn't right. If all your parts are xs650 parts then no spacer is needed. If some of the parts came off other bikes, they may bolt on but need adaptations to work.