For 95% of carbs, opening the screws is richer. 2-1/2 should be on the rich side, but that is good for initial starting. Once the engine is warm you can work on leaning the mixture to get the most consistent idle at about 650RPM. Try to keep the screws the same number of turns out. If you start altering them individually, you can end up with one bore carrying the engine and the other doing nothing.

For electric chokes, you must know that the choke starts slowly opening from the time the ignition switch is turned on. In other words, the choke has nothing to do with the temperature of the engine, only the amount of time you have the switch in run. If the engine will not start right off, but after sitting with the ignition on for a minute it does, then it implies your choke may be set too rich. Loosen and turn the dial a click or two to the lean direction.

If the above does not help...there is a chance the fuel pressure is too high, so the float is being overpowered. You should be getting no more than 6psi while cranking or running.