Grease the frizzen foot where it bears on the spring. Use something like chassis lubricant "gun grease". Even oil may not work well.
If the lock came direct from Chambers and the frizzen is too soft then you need to contact them.
Is the frizzen too soft the frizzen will hang up when the flint cuts into it too deeply.
It is possible, likely even, the mainspring is too weak.
Its possible the cock needs to be slightly bent to put a slight down angle on the flint.
In any case the lock needs to be looked at by someone who knows how to make it work right.
Dan