Does it have a stator winding? (to charge a battery)
I'm just winging this without reviewing the previous pages, I'm thinking it was a 12 hp engine on a mower and you are hand cranking it.
Is it set up for electric start on a riding mower?
If so make sure the stator wires are not grounded or shorted if it has a stator for such.
The stator would be under the flywheel and couple wires hanging out and it has some plastic and electrical coils and would probably produce white smoke and weird plastic smell for awhile and might even melt and get into the flywheel if it's burning or getting hot.
Might just be some grease burning off the block but might have to lift the cowling and take a peek if it don't have a stator.
Some of the briggs electric start can be started electrically with the cowling off. Do not operate one with the air cowling off for more than few seconds or they will overheat.