actually your flinter should throw good sparks with out the frizzen spring installed.
with the frizzen closed and the cock (hammer) in the half cock position the flint should be close enough for a dollar bill to fit between the face of the flint and the face of the frizzen.
if the flint touches the face, then you can dress the flint face by knapping or use a bench grinder to slowly dress the rear of the flint while using water to keep the flint cool.
the flint should strike as close to the top of the frizzen as possible and scrape down the face of the frizzen. the flint will actually remove small shavings of metal and that is what lands in the flash pan to ignite the powder.
some folks place the flint in the cock jaw with the bevel down @ the instructions of the 18th century english army or place the flint with the bevel up. the important thing is that the flint is square to the frizzen face and striking as high as possible.
then there's the controversy over what to wrap around the flint to help grip
in the cock jaw. some use leather other's swear by lead.
a good attack angle for the flint strike of the frizzen is roughly 60'.
this can be accomplished by heating the cock and bending it forward or backward. a throated cock ...one with a bottom connection from the bottom jaw to the main stem has to have the metal connection at the bottom of the cut out (throat) sawed or cut to allow the cock to be bent then re-attached, (welded).
make sure frizzen face is devoid of grease and powder residue & the flint face too.
you can field knap the flint with the flint still in the cock by holding the frizzen almost open with your thumb behind so the frizzen will not move and cock and let the flint fall against the bottom edge of the frizzen to knap to a new edge.
hope this helps