If you have to choke a warm engine, it's lean, not rich (flooding is too rich). Use an unlit Propane torch around the carburetor base, intake manifold, vacuum hoses etc. to find your vacuum leak. Then fix it. That hissing noise is caused by air getting into the engine that's not going through the carburetor to get the proper amount of gasoline mixed with it.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!