Should the ball bearing thats identified as part 3 rotate smoothly? or because it is groved does it have uniformed positions that there are pauses on it?

Think i may have the answer myself now that i have paid attention to what it's connecting to! It's the alternator drive shaft bearing if i am not mistaken... Which would suggest it should rotate smoothly all the way round!

Best i add one to my shopping list...

I wonder if this was the cause of the rumble that i was getting when there was no drive applied and was coasting?!

um ....you really sure you need to ask twincarb ? lol yes mate all bearing should be silent running .

alby mentioned something similar ...after his fix to the same bearing ...his bike runs amazingly smooth and quiet

hmmmmm lets just say i am having a special moment here!

Have got the offending item in my hands at the moment... time to see if i can source a replacement

im guessing it should be a pretty common component mate ....unlike some of the "output shaft" and "swingarm " stuff

tc - just go to your local bearing dealer.
some bearing info here

http://hrsbstaff.ednet.ns.ca/bvogel/K100/download/bearings_equivalency_chart.htm