Green’s Dictionary of Slang

blubber n.¹

(UK Und.) the mouth.

1725		New Canting Dict. n.p.: blubber, the Mouth.
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: Blubber, the mouth, (cant).
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.

In phrases

stop someone’s blubber (v.)

(UK Und.) to silence, poss. by murder.

1725		New Canting Dict. n.p.: I’ve stopt his Blubber; I’ve stopt his Mouth. I’ve done his Business, He’ll tell no Tales, &c.
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. 1725].
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: I have stopped the cull’s blubber; I have stopped the fellow’s mouth, meant either by gagging or murdering him.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1862		E. de la Bédollière Londres et les Anglais 313/1: blubber, [...] bouche. I have stopped the fellow’s blubber; je lui ai fermé la bouche.