Check the carb, inlet or bowl could be blocked with evaporated oil or pick up could have something blocking it.

If carb is clean and un-blocked check the reeds, if it has any.

Also pull the pipe they have habit of carboning up to the point of being closed.

Is fuel leaking by the float needle and flooding it? I'm presuming that's why you did the petcock.
If flooding isn't the issue, and there is nothing floating around plugging a jet, I'd do a compression test.

OK, so we know we have a fuel issue to fix.
Ethanol is the problem. Many-many flooding problems since ethanol.
The fix so far is to shut the fuel off and let the carb run/drain dry.
Running non ethanol surely would be a plus.
Iv'e been recommending a inline shut off close to the carb. I install a filter right above it just cuz.
So far it's helped. I'm thinking that the fuel running in cleans the ethanlol gunk off the needle and allows it to operate normal (not sticking).