Filling a Holley with water.
Had a nice rebuilt and balanced 351W
4V and read that it was possible to decarbon an engine by dribbling water into it when running to make cleansing steam.
No idea why I thought it needed it but decided to give it a go anyway.
Air cleaner off, 2500 rpm, slopped the jug of water into it by mistake.
Stumbled and coughed, steam came out of a few gaskets, never ran quite the same afterwards.