Can you kill the engine with the choke only?
If not, or it's hard to kill with the choke you have a vacuum leak.
From your answer about the hand over the carb choke making it run better it should still come off for an inspection and cleaning.
If I manually set the choke (there is no choke linkage I have to do it under hood myself) and start it up she runs at 4,000 RPM immediately on start up
If I loosen the choke screw and set the choke then starat it up, she'll be at 4,000RPM for 1-3 seconds before the vibrations from the engine shakes the choke off and then the engine dies (too much air???)
The engine won't run without the choke on
But with choke it's always above 3,000RPM (no tach, just guessing by sound)