In cold weather it is necessary to introduce a larger amount of fuel to mix with the cold air.
This is accomplished by closing the choke valve #25, which produces more vacuum at the nozzle so additional fuel will be introduced to the manifold.
Some applications include a relief valve #25. To prevent an over rich condition, the relief valve will open when the choke valve is fully closed and engine RPM increases. This introduced more air and acts more like an automatic choking action.
To avoid too much fuel entering the engine, the choke valve must be opened once the engine is warm.
Adjusting the idle mixture screw should be done only after the engine is warmed up.
Check the relief valve. It may be stuck closed. The spring may be missing or broken. The spring is not available, so when missing a more manual control of the choke will be necessary.
Fuel leaking out of the throttle shaft. When cold too much choking will cause this to happen. When the engine is warm and the choke is open there should be no fuel coming out of the throttle valve. If so, then you have a flooding condition.