Honda-SOHC

Hello all, can someone please give me some advice about a problem with my 400 four that I am restoring? On tick over there is a knocking noise coming from the bottom end (quite bad). This goes off when the revs are raised. It is the same when hot or cold. I have split the engine and all of the shells look ok and there seems to be no play on the conrods. The crank journal shells also have very little rub marks. Any ideas? Some one suggested that it may just be the carbs that needed balancing. Also can someone tell me how if or how you check the primary chain needs replacing?

Thanks
Steve