When I got my '53 running after 25 years of standing still, I also lived through a fine big BOOM when it first started to fire. Without the wisdom of this site, I concluded that during all those years mice and related vermin had plugged the exhaust system as well as filling every other orifice available. I ended up working on the motor for a few weeks before trying to fire it up again. By that time I had a new standard assortment muffler installed and it hasn't exploded since.
I would consider that those years of weed control duty might have led to a plugged exhaust.
