Small Engines (Lawn Mowers, etc.): B & S bad coil, air gap, necessary voltage

Question
I was checking for spark and felt only a very weak pulse using a screwdriver in hand trick. It was actually hard to feel it, so I then attached the spark plug and couldn't even see a spark. I assume the coil is bad, but before I spend the $30 bucks on a new coil I would just like to know if there are any ways to verify that that is the problem. I've done a fair amount of small motor work but never had a bad coil, so its new to me.

Answer
I've only had one weak coil, very similar to what you described.  Briggs, and several other companies, sell inline spark testers with a 0.166 thousandth of an inch air gap that simulates the necessary voltage to fire under compression.

The weak coil I had would barely shock you but when I checked it wiht the inline spark tester the coil would not produce spark.  Replaced coil and the engine ran fine.

From what you described, I'm betting the coil is bad.
Eric