Does the engine have the internal rotor/ external stator? If yes should have 3 lines on the stator, the mark on the rotor should line up with the longest line on the stator at 2.7mm BTDC.I have done this many a time on a YZ 80 ignition always works out right.The internal stator/external flywheel type usualy has 2 marks on the flywheel at TDC the second mark usualy is smack bang underneath the trigger.
HTH