Small Engines (Lawn Mowers, etc.): Got fire but wont crank, flywheel, armature

Question
I have a Briggs 5hp tiller. I've replaced the armature with a new one that does away with points. I even replaced the spark plug. I've got fire & it even fired up once, but it was only for about 3 seconds then it shut off. Now it won't crank up at all. It kinda sounds like it wants to, but it just don't. I was guessing the problem must be in the carb, but it is an in-line carb & I don't know where to begin or if that's even the problem. I'd be very grateful for any kind of help. thnx

Answer
I am going to make a guess here, just from seeing it before.  I am guessing in your working on this engine that you have had the clutch off, and maybe the flywheel.  Then when the clutch was reinstalled,
that it wasn't tight enough, and you have sheared the flywheel key.
You then have spark, but at the wrong time.  Take a look and let me know, and we can get more into it.