A few things loose in my head

In my Kwacker the is a clunk sound in the head at idle, there is 2 things i can think of, 1. Slack timing chain, where as my bike has the Automatic cam chain testioner,which is known for sticking. would changing this to a APE manual one help?, 2. there is play between the valve tappets and the cam lobes, should there be valve shims installed to take out some of the play. the bike runs like a charm, it's only at idle that i can hear this noise and it drives me nutts.

If the engine gets really quiet have your valve clearance checked. Its normal to have some valve chatter but not bangs and clunks. Check with the tech tips about valve clearance and why you need to check them

Remove the automatic chain tensioner,clean it and look for binding parts. It is operated by oil pressure and any grit will cause things to stick.

A good solvent is kerosene as it has a high flash point and is not as toxic as gasoline. Use a small clean paint brush and rubber gloves in a well ventilated area.

in addition to a loose chain, if the carbs are out of sink it can cause some rattle noise form the top end