This is what you do. Bring the piston all the way to the top of the cylinder by turning the crankshaft. There will be a mark on the crank gear and the cam. Use these as guides. Rotate the crank and follow the engine strokes to check the timing.
What kind of problems are you facing and why do you suspect a timing problem on your Honda lawn mower? Are you sure it's no other problem. Can you describe what exactly is happening?