From MopedWiki

Timing can refer to several things on a moped.

• Ignition timing, or when the spark plug fires in relation to the piston's position in the cylinder.
• Port timing, or when the ports in the cylinder are opened and closed by the piston

Some helpful timing-related articles:

• Guide to Motobecane spark and timing (ignition timing)
• Calculating timing (port timing)
• Ignition Timing Chart for Puch
• Peugeot Timing Guide (ignition timing)
• Fred's Guide (ignition timing)