The adjustable magneto plate allows you to retard your base ignition timing by up 15 degrees. This is especially helpful with high rpm (9k+) engines, it will increase rpm and decrease heat in the cylinder.
Use the slotted holes to bolt the plate to the case, rotate to your desired timing, bolt the magneto onto the plate with the remaining 2 holes. Each line represents 3.75°.
You may need to grind down the case to rotate the magneto fully.
WARNING: use at your own risk! Messing with ignition timing can cause damage if you do not know what you are doing.