Honda SH300 2006 Manual page 439

The ignition timing is correct if the "F" mark on the
flywheel aligns with the index mark on the right
crankcase cover at idle.
Increase the engine speed and make sure the "F"
mark begins to move.
Apply engine oil to the timing hole cap threads and
seating surface.
Coat a new O-ring with engine oil and install it onto
the timing hole cap.
Install the timing hole cap and tighten it.
TORQUE: 6 N·m (0.6 kgf·m, 4.4 lbf·ft)
IGNITION SYSTEM
"F" MARK
TIMING HOLE
CAP
INDEX MARK
O-RING
20-9