I know alot of people who have HJC helmets suffer the problem of the visor opening during high speed shoulder checks..
Well heres my solution to the problem.
1) first you will need to find some plastic approx 1/16 inch thick. Some thing you can cut with cutters.
2) you will need a pair of needle nose pliers and cutters.
3)remove your visor and locate the slot indacated by the white arrow.It is the lower tension tabs that keep the visor shut.
4)cut a piece of plastic just bigger than the slot..use your needle nose's to push it into the slot.this applies more tension to the tab on the visor when its in the closed position.
5)add a drop of crazy glue to hold the piece into position .
When you close your lid you will notice its alot more firm and locks more tightly. This works for me on my CL-12 and AC-10 ..Hope This helps you as well!