bigted, the Briggs test for whether the flywheel magnet still has enough magnetism is to put the flat end of a 10" long flat blade screwdriver on the magnet, then lift the flywheel and see if the magnet securely holds the screwdriver. It sounds as if the one you were using didn't pass it.

Here is the full Briggs FAQ on magneto theory:
http://eu-en.myfaqcenter.com/Answer/?p_faqid=3805

tiger, the clearance is measured to the plain surface of the flywheel, not the magnet part. Also, you need to have equal gaps to the two sides of the magnetic yoke.