you set both the inlet and exhaust valve clearances on the compression stroke with the piston at top dead centre.so basically turn the engine over by hand in the direction it runs in until the inlet valve opens and then closes this will be on a downward stroke the next stroke upwards will be the compression stroke so when the piston gets exactly to the top of the stroke that is where you check the valve clearances you can put a screwdriver in the hole the spark plug goes in to tell when it is at the top or there should be a mark on the flywheel also that lines up with a mrark on the crankcase when it is at top dead centre usually it has a t next to it do not use the f mark as this is before top dead centre,but i would rely on the screwdriver in the plug hole for a more accurate reading.ok its easier than it sounds,good luck ,adam.
adam bike doctor
April 2006