Choke Opens Too Fast
It might be the choke was not set tight enough when cold. When cold, the choke valve should take a small amount of pressure to open it using your finger.
Did the hot wire get hooked up to something that is 12v only when the key is on?
It could be it wasn’t adjusted correctly.
Hold the throttle open.
Turn the thermostat so that it closes the choke valve. When closed give it another 1/8″ to preload it.
Without starting the engine, turn the key to on position. The choke should slowly start to open. If it opens too fast, then the thermostat may be bad.