If you are not familiar with the SOHC4 CB650 there were a lot of changes made in the 4 years of (US market) production. It can make finding parts difficult, if you are looking to make it "original".
Off the top of my head:
1979 CB650 only 1 model completely different than other years for US bikes.
1980 CB650 and CB650C Same engine as ’79 different model # on carbs from ’79, but interchangeable.
C has 2” longer forks than standard model, 4 into 4 pipes, Comstar wheels, chrome headlight bucket, different side cover emblems, 40 tooth rear sprocket
Standard model has 4 into 2 pipes, spoke wheels, and black plastic headlight bucket 39 tooth rear sprocket
1981 Different carbs than ’79 and ’80 models carbs not compatible with earlier years. Engine head changed to match carb spacing. The petcock fuel line size changed to match the carbs. Petcock bung size on fuel tank changed too.
C got air assist forks and dual disc front brakes
Standard model otherwise the same as ‘80
’82 standard pretty much the same as ‘81
C discontinued and SC (Nitehawk) introduced
The '81 models had pressed in jets in the carbs, and the '82 had screwed in jets...
