You should see the ignition pickup (sensor) attatched to the engine just behind the prop hub. Pull the engine over till it's at TDC. Now you see the magnet. Loosen the screws that hold the sensor and slide it a little ways towards the magnet. That will reduce timing.
There are two types of ignition units. One needs to be about 5mm+- center of magnet to center of sensor. The other type like CH and rcxl are adjusted to about 28*.
CH website has instructions for setting timing. http://www.ch-ignitions.com/MENU.html