It sounds almost as if the position of the coil, in relation to the flywheel has been fractionally adjusted. Just fixed a very similar problem on my Mountfield.
I used a mutimeter to verify the functionality of the coil, if you have the presence of an electrical current when the cord is gently pulled, the coil is ok.
Next I loosened the clamping bolts, that hold the coil in its popsition. Next, fold a piece of A4 paper in half, place the paper between the points and the flywheel, and rotate the flywheel until the magnets pull the loosened coil tight up against it Retighten the coils clamping bolts, locking it into its proper position. Remove the sheet of paper, and verify that a spark is now being produced.
This should, hopefully, solve your problem.
Good luck.!
oldkezza@live.co.uk
kezza
November 2008