Several things come to mind, none are good and some are less good than others:
1>
NEVER - NEVER put cool or cold coolant into an overheated engine while it is not running and circulating/mixing the different temperature liquids, as the shock of the cold water contacting the VERY, VERY HOT cast iron of the heads, intake, block, etc, can and often does cause cracking and or warpage.
See below.
2>Vacuum leak due to:
A>Faulty intake gasket caused by warping of something.
B>Cracked or warped intake manifold.
C>Cracked or warped head.
D>Blown head gasket.
E>Cracked or warped block.
F>Any or all of the above.
3>MAYBE, just MAYBE (if you are really lucky, depending on your setup)you created a fairly substantial vacuum at or near the base of your carburetor.
This is likey not the kind of stuff you were hoping to hear, but you asked!
Gene