[black350]

I could use some help figuring out the source of this issue and a solution. This is a 71 CB350 I was attempting to start. Almost immediately after hitting the starter button the knocking sound can be heard and you can see how the cam stutters and stops. I recently adjusted the clutch cable, cam chain, valve clearance, and points and to the best of my knowledge everything was done correctly and to spec. It was also making this sound before the adjustments. There isn't any knocking when using the kickstart, or turning the rotor.

 

[Yendor]

Usually this means the Sprag Clutch for the starter motor that is in the Stator is going bad.

It is a simple job to replace the Rollers, Springs & Pins.

If you look at the inside of the Stator you can see the Rollers that engage the shaft.
Once the Crank Shaft gets up to speed the spinning force overrides the springs and the rollers pull away from the shaft.

PS: the Springs Pic is mostly OLD worn parts.
(1) New Pin & Spring

 

[76TWIN]

I second the starter clutch as well.