Please do yourself a favor and DONT MESS with the frizzen spring.  Your best bet is to have a gunshith very familiar with flinters tune your piece.  You may also send just the lock if necessary.  If you need a good smith, let me know.  I have a guy work mine and trust no other.   I have a 1700's american smooth rifle, .72cal, custom made hand built replica.  
Hope this helps!