I have done some research on these models from original factory workshop manuals, it seem the only accurate way to find TDC is by attaching dial gauge via spark plug hole, for ignition timing rotate the crank and set the gauge to 0.8 mm BTDC then adjust the back plate, it sounds odd l now no degrees but this is the procedure listed in the archives for general publication, there appears to be no timing marks on engine other than cam dots which are set after you establish TDC, valves are also set at the TDC compression stroke both valves closed.