The amount of sparks will depend in part on how many little sharp points on the edge of the flint hit the frizzen, and this will vary as the frizzen wears, will vary from flint to flint. But the frizzen flint does have to have sharp points. If it is dull, then it will not make many sparks. Changing small details like the length of the flint and whether the bevel of the flint is up or down can also make a difference in how well the flint works. By the way, flints can be resharpened. So, if your flint is dull, don't throw it away. Just ask on here how to sharpen it.
Be sure that the flint is slid all the way into the jaws, so that it sits against the top jaw screw. Use leather folded around the flint to help the jaws grip the flint, but cut a little hole in the middle of the leather so that the flint can slide back and sit against the top jaw screw. That helps all the energy from the strike go into making sparks. If, instead, you have a cushion of leather behind the flint, then the leather will soften the strike. You don't want that. Cutting a little hole in the leather can help a lot.
It can be helpful to test a frizzen in dim light, almost dark, so that you can see the sparks. I also find it helpful to make a short video in dim light, using my phone, and then look at the video frame by frame. That helps me see exactly how the sparks are falling. You want the majority of them to fall into the pan.
CORRECTED TYPO: frizzen flint
Sorry for any confusion!
