How to find the valve number of 7.5 HP gasoline engine?

The only thing that is not marked is the statement of top dead center. You can get down to the spark plug, turn the flywheel, see the piston in the highest position from the spark plug hole, and then you can adjust the valve.

Skilled people can directly feel when turning the flywheel, that is, there is resistance when rotating at the compression point. After the flywheel passes through the resistance point, there is a relaxation point. When the valve rotates slightly back and forth at that relaxation point, the valve will not change. The point is also the top dead center, and the valve can be adjusted.

Boxin parts are designed for reference.