Chafing Noise in Valve Cover

Hi Everyone - I'm at a loss here:
1981 XJ550 Seca.
Trying to diagnose an issue: at around 4000 - 4500 rpm I hear a chafing noise on the right side underneath the cam cover (yes, I'm using a very technical term) and in 6th gear I won't go over 55 mph and feels there is no power.
Cam chain not tight enough?
I replaced the valves recently but same issue.
Totally stumped on this - please help - I do love my Seca and want to rider her for the summer.
Thank you

 

Is the cam chain adjuster fully extended? Is it an automatic or manual adjuster? Remove cam cover to check for slack in chain. Tachometer drive cable gear in the cam cover worn? Disconnect the cable to see if the noise is still there, might be the tachometer unit you hear. Is the clutch cable adjusted property? It's more likely to slip accelerating than in 6th gear l think. Have you checked valve clearances recently and synchronised the carburettors after the clearances were correct? Do you have a Haynes manual for your bike?

 

Check out your chain and battery, if they are fine enough then you need to visit a mechanic or dealer.