Most of the carbs with idle scres that controlled air have a left hand thread. So turning them clockwise moves them out, leaning the mixture. This was to make it less confusing as turning a standard idle mix screw clockwise reduces the idle fuel mix.
Check at the voltage regulator. If it is 'seeing' 13 volts, when the voltage at the alternator output is 15, its because there is resistance in the wiring. The regulator is doing the correct thing based on the information it is getting (system voltage is lower than target of approx 14.2 Volts).
Not likely the issue based on the situation.
That's plenty. Gravity feed is fine for putting around. It just needs to keep the bowl full. It may be a little low since the pressure on the needle is a little less. Float setting is important but again since it was running before it doesn't point to this as the problem of dying in gear.