Problem turned out to be a loose inlet valve seat. Inlet valve seat successfully punched and peened in place as per B&S guide. Re-lapped valve and seats (on both valves). Following rebuild motor starts first time every time and no recurrence of the noise during two ten minute runs. A good sign i...

Thanks. My governor 'plate' is plastic rather than metal and there is no sign of damage to it or flywheel. If my use of the word clacking implies not metallic then I have used the wrong word. The noise definitely sounds metallic.
Many Thanks

Thanks for a great suggestion. I will check. The noise sounds more metallic and my thinking was it is more valve related but I couldn't see a valve seating problem unless it only shows up when hot. Do you have experience of the governor hitting something or making/initiating a loud clanging noise? M...

I don't know the exact age of this machine but as label says Birmid Qualcast (H&GE) Ltd I assume it is 1980s. Part No is L23981, Serial No. 039643/I. Electronic ignition and delOrto carburettor. Engine No. G 581132. Can anyone confirm age? However my real problem is that after a few minutes the ...