Generally what i do is pull the valve caps then rotate it until the mark lines up, but if you don't have access to the timing mark because the plug is stuck pull the pulse rotor cover off and spin it around until the advancer and pickup are lined up, thats the F on the flywheel, the T is just a smidge past that point. But i have adjusted the valves with it set to the F going by the advancer and its just fine as thats the top of the compression stroke minus a few degrees, perfectly fine doing it that way.
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1984 Honda ATC200ES "Big Red"
1982 ATC200E "Hondie"
1988 TRX300FW "Project Quad" Still in progress....